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      1  1.1  christos <!DOCTYPE html>
      2  1.1  christos <html lang="en">
      3  1.1  christos <head>
      4  1.1  christos <title>Sources for time zone and daylight saving time data</title>
      5  1.1  christos <meta charset="UTF-8">
      6  1.1  christos </head>
      7  1.1  christos <body>
      8  1.1  christos <h1>Sources for time zone and daylight saving time data</h1>
      9  1.1  christos <p>
     10  1.1  christos <a href="https://en.wikipedia.org/wiki/Time_zone">Time zone</a> and
     11  1.1  christos <a href="https://en.wikipedia.org/wiki/Daylight_saving_time">daylight-saving</a>
     12  1.1  christos rules are controlled by individual
     13  1.1  christos governments. They are sometimes changed with little notice, and their
     14  1.1  christos histories and planned futures are often recorded only fitfully. Here
     15  1.1  christos is a summary of attempts to organize and record relevant data in this
     16  1.1  christos area.
     17  1.1  christos </p>
     18  1.1  christos <h2 id="tzdb">The <code><abbr title="time zone">tz</abbr></code> database</h2>
     19  1.1  christos <p>
     20  1.1  christos The <a href="https://en.wikipedia.org/wiki/Public_domain">public-domain</a>
     21  1.1  christos time zone database contains code and data
     22  1.1  christos that represent the history of local time
     23  1.1  christos for many representative locations around the globe.
     24  1.1  christos It is updated periodically to reflect changes made by political bodies
     25  1.1  christos to time zone boundaries and daylight saving rules.
     26  1.1  christos This database (known as <code><abbr>tz</abbr></code>,
     27  1.1  christos <code><abbr>tzdb</abbr></code>, or <code>zoneinfo</code>)
     28  1.1  christos is used by several implementations,
     29  1.1  christos including
     30  1.1  christos <a href="https://www.gnu.org/software/libc/">the
     31  1.1  christos <abbr title="GNU's Not Unix">GNU</abbr>
     32  1.1  christos C Library</a> (used in
     33  1.1  christos <a href="https://en.wikipedia.org/wiki/Linux"><abbr>GNU</abbr>/Linux</a>),
     34  1.1  christos <a href="https://www.android.com">Android</a>,
     35  1.1  christos <a href="https://developer.mozilla.org/en-US/docs/Mozilla/B2G_OS">B2G
     36  1.1  christos <abbr title="Operating System">OS</abbr></a>,
     37  1.1  christos <a href="https://www.freebsd.org">Free<abbr
     38  1.1  christos title="Berkeley Software Distribution">BSD</abbr></a>,
     39  1.1  christos <a href="https://netbsd.org">Net<abbr>BSD</abbr></a>,
     40  1.1  christos <a href="https://www.openbsd.org">Open<abbr>BSD</abbr></a>,
     41  1.1  christos <a href="https://www.chromium.org/chromium-os">Chromium OS</a>,
     42  1.1  christos <a href="https://cygwin.com">Cygwin</a>,
     43  1.1  christos <a href="http://www.delorie.com/djgpp/"><abbr
     44  1.1  christos title="DJ's GNU Programming Platform">DJGPP</abbr></a>,
     45  1.1  christos <a href="https://en.wikipedia.org/wiki/MINIX">MINIX</a>,
     46  1.1  christos <a href="https://www.mysql.com">MySQL</a>,
     47  1.1  christos <a href="https://en.wikipedia.org/wiki/WebOS"><abbr
     48  1.1  christos title="Web Operating System">webOS</abbr></a>,
     49  1.1  christos <a href="https://ibm.com/aix"><abbr
     50  1.1  christos title="Advanced Interactive eXecutive">AIX</abbr></a>,
     51  1.1  christos <a href="https://en.wikipedia.org/wiki/BlackBerry_10">BlackBerry 10</a>,
     52  1.1  christos <a href="https://www.apple.com/ios/"><abbr
     53  1.1  christos title="iPhone OS">iOS</abbr></a>,
     54  1.1  christos <a href="https://www.apple.com/macos/">macOS</a>,
     55  1.1  christos <a href="https://www.microsoft.com/en-us/windows">Microsoft Windows</a>,
     56  1.1  christos <a href="https://www.hpe.com/info/openvms">Open<abbr
     57  1.1  christos title="Virtual Memory System">VMS</abbr></a>,
     58  1.1  christos <a href="https://www.oracle.com/database/index.html">Oracle Database</a>, and
     59  1.1  christos <a href="https://www.oracle.com/solaris">Oracle Solaris</a>.</p>
     60  1.1  christos <p>
     61  1.1  christos Each location in the database represents a region where all
     62  1.1  christos clocks keeping local time have agreed since 1970.
     63  1.1  christos Locations are identified by continent or ocean and then by the name of
     64  1.1  christos the location, which is typically the largest city within the region.
     65  1.1  christos For example, <code>America/New_York</code>
     66  1.1  christos represents most of the <abbr title="United States">US</abbr> eastern time zone;
     67  1.1  christos <code>America/Phoenix</code> represents most of Arizona, which
     68  1.1  christos uses mountain time without daylight saving time (<abbr
     69  1.1  christos title="daylight saving time">DST</abbr>);
     70  1.1  christos <code>America/Detroit</code> represents most of Michigan, which uses
     71  1.1  christos eastern time but with different <abbr>DST</abbr> rules in 1975;
     72  1.1  christos and other entries represent smaller regions like Starke County,
     73  1.1  christos Indiana, which switched from central to eastern time in 1991
     74  1.1  christos and switched back in 2006.
     75  1.1  christos To use the database on an extended <a
     76  1.1  christos href="https://en.wikipedia.org/wiki/POSIX"><abbr
     77  1.1  christos title="Portable Operating System Interface">POSIX</abbr></a>
     78  1.1  christos implementation set the <code><abbr>TZ</abbr></code>
     79  1.1  christos environment variable to the location's full name,
     80  1.1  christos e.g., <code><abbr>TZ</abbr>="America/New_York"</code>.</p>
     81  1.1  christos <p>
     82  1.1  christos Associated with each region is a history of offsets from
     83  1.1  christos <a href="https://en.wikipedia.org/wiki/Universal_Time">Universal
     84  1.1  christos Time</a> (<abbr>UT</abbr>), which is <a
     85  1.1  christos href="https://en.wikipedia.org/wiki/Greenwich_Mean_Time">Greenwich Mean
     86  1.1  christos Time</a> (<abbr>GMT</abbr>) with days beginning at midnight;
     87  1.1  christos for time stamps after 1960 this is more precisely <a
     88  1.1  christos href="https://en.wikipedia.org/wiki/Coordinated_Universal_Time">Coordinated
     89  1.1  christos Universal Time</a> (<abbr>UTC</abbr>).
     90  1.1  christos The database also records when daylight saving time was in use,
     91  1.1  christos along with some time zone abbreviations such as <abbr>EST</abbr>
     92  1.1  christos for Eastern Standard Time in the <abbr>US</abbr>.</p>
     93  1.1  christos <h2 id="download">Downloading the <code><abbr>tz</abbr></code> database</h2>
     94  1.1  christos <p>
     95  1.1  christos The following <a
     96  1.1  christos href="https://en.wikipedia.org/wiki/Unix_shell">shell</a> commands download
     97  1.1  christos the latest release's two
     98  1.1  christos <a href="https://en.wikipedia.org/wiki/Tar_(computing)">tarballs</a>
     99  1.1  christos to a <abbr>GNU</abbr>/Linux or similar host.</p>
    100  1.1  christos <pre style="margin-left: 2em"><code>mkdir tzdb
    101  1.1  christos cd tzdb
    102  1.1  christos <a href="https://www.gnu.org/software/wget/">wget</a> https://www.iana.org/time-zones/repository/tzcode-latest.tar.gz
    103  1.1  christos wget https://www.iana.org/time-zones/repository/tzdata-latest.tar.gz
    104  1.1  christos <a href="https://www.gnu.org/software/gzip/">gzip</a> -dc tzcode-latest.tar.gz | <a href="https://www.gnu.org/software/tar/">tar</a> -xf -
    105  1.1  christos gzip -dc tzdata-latest.tar.gz | tar -xf -
    106  1.1  christos </code></pre>
    107  1.1  christos <p>Alternatively, the following shell commands download the same
    108  1.1  christos release in a single-tarball format containing extra data
    109  1.1  christos useful for regression testing:</p>
    110  1.1  christos <pre style="margin-left: 2em"><code>wget <a href="https://www.iana.org/time-zones/repository/tzdb-latest.tar.lz">https://www.iana.org/time-zones/repository/tzdb-latest.tar.lz</a>
    111  1.1  christos <a href="https://www.nongnu.org/lzip/">lzip</a> -dc tzdb-latest.tar.lz | tar -xf -
    112  1.1  christos </code></pre>
    113  1.1  christos <p>These commands use convenience links to the latest release
    114  1.1  christos of the <code><abbr>tz</abbr></code> database hosted by the
    115  1.1  christos <a href="https://www.iana.org/time-zones">Time Zone Database website</a>
    116  1.1  christos of the <a href="https://www.iana.org">Internet Assigned Numbers
    117  1.1  christos Authority (IANA)</a>.
    118  1.1  christos Older releases are in files named
    119  1.1  christos <code>tzcode<var>V</var>.tar.gz</code>,
    120  1.1  christos <code>tzdata<var>V</var>.tar.gz</code>, and
    121  1.1  christos <code>tzdb-<var>V</var>.tar.lz</code>,
    122  1.1  christos where <code><var>V</var></code> is the version.
    123  1.1  christos Since 1996, each version has been a four-digit year followed by
    124  1.1  christos lower-case letter (<samp>a</samp> through <samp>z</samp>,
    125  1.1  christos then <samp>za</samp> through <samp>zz</samp>, then <samp>zza</samp>
    126  1.1  christos through <samp>zzz</samp>, and so on).
    127  1.1  christos Since version 2016h, each release has contained a text file named
    128  1.1  christos "<samp>version</samp>" whose first (and currently only) line is the version.
    129  1.1  christos The releases are also available in an
    130  1.1  christos <a href="ftp://ftp.iana.org/tz/releases/"><abbr
    131  1.1  christos title="File Transfer Protocol">FTP</abbr> directory</a> via a
    132  1.1  christos less-secure protocol.</p>
    133  1.1  christos <p>Alternatively, a development repository of code and data can be
    134  1.1  christos retrieved from <a href="https://github.com">GitHub</a> via the shell
    135  1.1  christos command:</p>
    136  1.1  christos <pre style="margin-left: 2em"><code><a href="https://git-scm.com">git</a> clone <a href="https://github.com/eggert/tz">https://github.com/eggert/tz</a>
    137  1.1  christos </code></pre>
    138  1.1  christos <p>
    139  1.1  christos Since version 2012e, each release has been tagged in development repositories.
    140  1.1  christos Untagged commits are less well tested and probably contain
    141  1.1  christos more errors.</p>
    142  1.1  christos <p>
    143  1.1  christos After obtaining the code and data files, see the
    144  1.1  christos <code>README</code> file for what to do next.
    145  1.1  christos The code lets you compile the <code><abbr>tz</abbr></code> source files into
    146  1.1  christos machine-readable binary files, one for each location. It also lets
    147  1.1  christos you read a <code><abbr>tz</abbr></code> binary file and interpret time stamps for that
    148  1.1  christos location.</p>
    149  1.1  christos <h2 id="changes">Changes to the <code><abbr>tz</abbr></code> database</h2>
    150  1.1  christos <p>
    151  1.1  christos The <code><abbr>tz</abbr></code> code and data
    152  1.1  christos are by no means authoritative. If you find errors, please
    153  1.1  christos send changes to <a href="mailto:tz (a] iana.org"><code>tz (a] iana.org</code></a>,
    154  1.1  christos the time zone mailing list. You can also <a
    155  1.1  christos href="https://mm.icann.org/mailman/listinfo/tz">subscribe</a> to it
    156  1.1  christos and browse the <a
    157  1.1  christos href="https://mm.icann.org/pipermail/tz/">archive of old
    158  1.1  christos messages</a>.</p>
    159  1.1  christos <p>
    160  1.1  christos If your government plans to change its time zone boundaries or
    161  1.1  christos daylight saving rules, inform <code>tz (a] iana.org</code> well in
    162  1.1  christos advance, as this will coordinate updates to many cell phones,
    163  1.1  christos computers, and other devices around the world. With
    164  1.1  christos less than a year's notice there is a good chance that some
    165  1.1  christos computer-based clocks will operate incorrectly after the change, due
    166  1.1  christos to delays in propagating updates to software and data. The shorter
    167  1.1  christos the notice, the more likely clock problems will arise; see "<a
    168  1.1  christos href="https://codeofmatt.com/2016/04/23/on-the-timing-of-time-zone-changes/">On
    169  1.1  christos the Timing of Time Zone Changes</a>" for examples.
    170  1.1  christos </p>
    171  1.1  christos <p>
    172  1.1  christos Changes to the <code><abbr>tz</abbr></code> code and data are often
    173  1.1  christos propagated to clients via operating system updates, so
    174  1.1  christos client <code><abbr>tz</abbr></code> data can often be corrected by
    175  1.1  christos applying these updates. With GNU/Linux and similar systems, if your
    176  1.1  christos maintenance provider has not yet adopted the
    177  1.1  christos latest <code><abbr>tz</abbr></code> data, you can often short-circuit
    178  1.1  christos the process by tailoring the generic instructions in
    179  1.1  christos the <code><abbr>tz</abbr> README</code> file and installing the latest
    180  1.1  christos data yourself. System-specific instructions for installing the
    181  1.1  christos latest <code><abbr>tz</abbr></code> data have also been published
    182  1.1  christos for <a href="https://www.ibm.com/developerworks/aix/library/au-aix-olson-time-zone/index.html"><abbr>AIX</abbr></a>,
    183  1.1  christos <a
    184  1.1  christos href="https://play.google.com/store/apps/details?id=com.google.android.timezone.data">Android</a>,
    185  1.1  christos <a
    186  1.1  christos href="http://userguide.icu-project.org/datetime/timezone"><abbr
    187  1.1  christos title="International Components for Unicode">ICU</abbr></a>,
    188  1.1  christos <a href="https://developer.ibm.com/javasdk/support/dst/jtzu/"><abbr>IBM</abbr></a>
    189  1.1  christos and <a
    190  1.1  christos href="http://www.oracle.com/technetwork/java/javase/tzupdater-readme-136440.html">Oracle</a>
    191  1.1  christos Java, <a href="http://www.joda.org/joda-time/tz_update.html">Joda-Time</a>, <a
    192  1.1  christos href="https://dev.mysql.com/doc/refman/en/time-zone-support.html">MySQL</a>,
    193  1.1  christos and <a
    194  1.1  christos href="https://nodatime.org/userguide/tzdb">Noda Time</a> (see below).
    195  1.1  christos </p>
    196  1.1  christos <p>Sources for the <code><abbr>tz</abbr></code> database are
    197  1.1  christos <a href="https://en.wikipedia.org/wiki/UTF-8"><abbr
    198  1.1  christos title="Unicode Transformation Format 8-bit">UTF-8</abbr></a>
    199  1.1  christos <a href="https://en.wikipedia.org/wiki/Text_file">text files</a>
    200  1.1  christos with lines terminated by <a href="https://en.wikipedia.org/wiki/Newline"><abbr
    201  1.1  christos title="linefeed">LF</abbr></a>,
    202  1.1  christos which can be modified by common text editors such
    203  1.1  christos as <a href="https://www.gnu.org/software/emacs/">GNU Emacs</a>,
    204  1.1  christos <a href="https://wiki.gnome.org/Apps/Gedit">gedit</a>, and
    205  1.1  christos <a href="https://www.vim.org">vim</a>.
    206  1.1  christos Specialized source-file editing can be done via the
    207  1.1  christos <a href="https://packagecontrol.io/packages/zoneinfo">Sublime
    208  1.1  christos zoneinfo</a> package for <a
    209  1.1  christos href="https://www.sublimetext.com">Sublime Text</a> and the <a
    210  1.1  christos href="https://marketplace.visualstudio.com/items?itemName=gilmoreorless.vscode-zoneinfo">VSCode
    211  1.1  christos zoneinfo</a> extension for <a href="https://code.visualstudio.com">Visual
    212  1.1  christos Studio Code</a>.
    213  1.1  christos </p>
    214  1.1  christos <p>
    215  1.1  christos For further information about updates, please see
    216  1.1  christos <a href="https://tools.ietf.org/html/rfc6557">Procedures for
    217  1.1  christos Maintaining the Time Zone Database</a> (Internet <abbr
    218  1.1  christos title="Request For Comments">RFC</abbr> 6557). More detail can be
    219  1.1  christos found in <a href="theory.html">Theory and pragmatics of the tz code and data</a>.
    220  1.1  christos </p>
    221  1.1  christos <h2 id="commentary">Commentary on the <code><abbr>tz</abbr></code> database</h2>
    222  1.1  christos <ul>
    223  1.1  christos <li>The article
    224  1.1  christos <a href="https://en.wikipedia.org/wiki/Tz_database">tz database</a> is
    225  1.1  christos an encyclopedic summary.</li>
    226  1.1  christos <li><a href="tz-how-to.html">How to Read the
    227  1.1  christos tz Database Source Files</a> explains the <code><abbr>tz</abbr></code>
    228  1.1  christos database format.</li>
    229  1.1  christos <li><a
    230  1.1  christos href="https://blog.jonudell.net/2009/10/23/a-literary-appreciation-of-the-olsonzoneinfotz-database/">A
    231  1.1  christos literary appreciation of the Olson/Zoneinfo/tz database</a> comments on the
    232  1.1  christos database's style.</li>
    233  1.1  christos </ul>
    234  1.1  christos <h2 id="web">Web sites using recent versions of the
    235  1.1  christos <code><abbr>tz</abbr></code> database</h2>
    236  1.1  christos <p>
    237  1.1  christos These are listed roughly in ascending order of complexity and fanciness.
    238  1.1  christos </p>
    239  1.1  christos <ul>
    240  1.1  christos <li><a href="https://time.is">Time.is</a> shows locations'
    241  1.1  christos time and zones.</li>
    242  1.1  christos <li><a href="https://www.timejones.com">TimeJones.com</a>,
    243  1.1  christos <a href="https://timezoneconverterapp.com">Time Zone Converter</a> and
    244  1.1  christos <a href="http://worldclock.com">The World Clock</a>
    245  1.1  christos are time zone converters.</li>
    246  1.1  christos <li><a
    247  1.1  christos href="http://twiki.org/cgi-bin/xtra/tzdatepick.html">Date and Time Gateway</a>
    248  1.1  christos lets you see the <code><abbr>TZ</abbr></code> values directly.</li>
    249  1.1  christos <li><a
    250  1.1  christos href="http://www.convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current
    251  1.1  christos Time in 1000 Places</a> uses descriptions of the values.</li>
    252  1.1  christos <li><a href="http://www.timezoneconverter.com/cgi-bin/tzc.tzc">Time Zone
    253  1.1  christos Converter</a>
    254  1.1  christos uses a pulldown menu.</li>
    255  1.1  christos <li><a href="http://home.kpn.nl/vanadovv/time/TZworld.html">Complete
    256  1.1  christos timezone information for all countries</a> displays tables of DST rules.
    257  1.1  christos <li><a href="https://www.timeanddate.com/worldclock/">The World Clock &ndash;
    258  1.1  christos Worldwide</a> lets you sort zone names and convert times.</li>
    259  1.1  christos <li><a href="https://24timezones.com">24TimeZones</a> has a world
    260  1.1  christos time map and a time converter.</li>
    261  1.1  christos <li><a href="https://www.zeitverschiebung.net/en/">Time Difference</a>
    262  1.1  christos calculates the current time difference between locations.</li>
    263  1.1  christos <li><a href="http://www.wx-now.com">Weather Now</a> and
    264  1.1  christos <a href="http://www.thetimenow.com">The Time Now</a> list the weather too.</li>
    265  1.1  christos </ul>
    266  1.1  christos <h2 id="protocols">Network protocols for <code><abbr>tz</abbr></code> data</h2>
    267  1.1  christos <ul>
    268  1.1  christos <li>The <a href="https://www.ietf.org">Internet Engineering Task Force</a>'s
    269  1.1  christos <a href="https://datatracker.ietf.org/wg/tzdist/charter/">Time Zone Data
    270  1.1  christos Distribution Service (tzdist) working group</a> defined <a
    271  1.1  christos href="https://tools.ietf.org/html/rfc7808">TZDIST</a>
    272  1.1  christos (Internet <abbr>RFC</abbr> 7808), a time zone data distribution service,
    273  1.1  christos along with <a href="https://tools.ietf.org/html/rfc7809">CalDAV</a>
    274  1.1  christos (Internet <abbr>RFC</abbr> 7809), a calendar access protocol for
    275  1.1  christos transferring time zone data by reference. The draft <a
    276  1.1  christos id="TZDIST-Geolocate"
    277  1.1  christos href="https://tools.ietf.org/html/draft-murchison-tzdist-geolocate-01">TZDIST
    278  1.1  christos Geolocate Extension</a> lets a client determine its time zone region
    279  1.1  christos from its geographic location using a <a
    280  1.1  christos href="https://tools.ietf.org/html/rfc5870">'geo' URI</a>.</li>
    281  1.1  christos <li>The <a href="https://tools.ietf.org/html/rfc5545">
    282  1.1  christos Internet Calendaring and Scheduling Core Object Specification
    283  1.1  christos (iCalendar)</a> (Internet <abbr>RFC</abbr> 5445)
    284  1.1  christos covers time zone
    285  1.1  christos data; see its VTIMEZONE calendar component.
    286  1.1  christos The iCalendar format requires specialized parsers and generators; a
    287  1.1  christos variant <a href="https://tools.ietf.org/html/rfc6321">xCal</a>
    288  1.1  christos (Internet <abbr>RFC</abbr> 6321) uses
    289  1.1  christos <a href="https://www.w3.org/XML/"><abbr
    290  1.1  christos title="Extensible Markup Language">XML</abbr></a> format, and a variant
    291  1.1  christos <a href="https://tools.ietf.org/html/rfc7265">jCal</a>
    292  1.1  christos (Internet <abbr>RFC</abbr> 7265)
    293  1.1  christos uses <a href="https://www.json.org"><abbr
    294  1.1  christos title="JavaScript Object Notation">JSON</abbr></a> format.</li>
    295  1.1  christos </ul>
    296  1.1  christos <h2 id="compilers">Other <code><abbr>tz</abbr></code> compilers</h2>
    297  1.1  christos <ul>
    298  1.1  christos <li><a href="https://sourceforge.net/projects/vzic/">Vzic</a> is a <a
    299  1.1  christos href="https://en.wikipedia.org/wiki/C_%28programming_language%29">C</a>
    300  1.1  christos program that compiles
    301  1.1  christos <code><abbr>tz</abbr></code> source into iCalendar-compatible VTIMEZONE files.
    302  1.1  christos Vzic is freely
    303  1.1  christos available under the <a
    304  1.1  christos href="https://www.gnu.org/copyleft/gpl.html"><abbr>GNU</abbr>
    305  1.1  christos General Public License (<abbr
    306  1.1  christos title="General Public License">GPL</abbr>)</a>.</li>
    307  1.1  christos <li><a href="https://sourceforge.net/projects/tzical/">tziCal &ndash; tz
    308  1.1  christos database conversion utility</a> is like Vzic, except for the <a
    309  1.1  christos href="https://www.microsoft.com/net">.NET framework</a>
    310  1.1  christos and with a <abbr>BSD</abbr>-style license.</li>
    311  1.1  christos <li><a
    312  1.1  christos href="http://search.cpan.org/dist/DateTime-TimeZone/">DateTime::TimeZone</a>
    313  1.1  christos contains a script <code>parse_olson</code> that compiles
    314  1.1  christos <code><abbr>tz</abbr></code> source into <a href="https://www.perl.org">Perl</a>
    315  1.1  christos modules. It is part of the Perl <a
    316  1.1  christos href="http://datetime.perl.org">DateTime Project</a>, which is freely
    317  1.1  christos available under both the <abbr>GPL</abbr> and the Perl Artistic
    318  1.1  christos License. DateTime::TimeZone also contains a script
    319  1.1  christos <code>tests_from_zdump</code> that generates test cases for each clock
    320  1.1  christos transition in the <code><abbr>tz</abbr></code> database.</li>
    321  1.1  christos <li>The <a href="https://howardhinnant.github.io/date/tz.html">Time Zone
    322  1.1  christos Database Parser</a> is a
    323  1.1  christos <a href="https://en.wikipedia.org/wiki/C%2B%2B">C++</a> parser and
    324  1.1  christos runtime library that is <a
    325  1.1  christos href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0355r4.html">moving
    326  1.1  christos forward</a> for inclusion in the next iteration of <a
    327  1.1  christos href="https://isocpp.org/std/the-standard"><em><abbr
    328  1.1  christos title="International Organization for Standardization">ISO</abbr>
    329  1.1  christos International Standard ISO/IEC 14882:2017(E) &ndash; Programming
    330  1.1  christos Language C++</em></a>.
    331  1.1  christos It is freely available under the
    332  1.1  christos <abbr title="Massachusetts Institute of Technology">MIT</abbr> license.</li>
    333  1.1  christos <li><a id="ICU" href="http://site.icu-project.org">International Components for
    334  1.1  christos Unicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a
    335  1.1  christos href="https://en.wikipedia.org/wiki/Java_%28programming_language%29">Java</a>
    336  1.1  christos libraries for internationalization that
    337  1.1  christos has a compiler from <code><abbr>tz</abbr></code> source
    338  1.1  christos and from <abbr title="Common Locale Data Repository">CLDR</abbr> data
    339  1.1  christos (mentioned <a href="#CLDR">below</a>)
    340  1.1  christos into an <abbr>ICU</abbr>-specific format.
    341  1.1  christos <abbr>ICU</abbr> is freely available under a
    342  1.1  christos <abbr>BSD</abbr>-style license.</li>
    343  1.1  christos <li>The <a href="https://github.com/lau/tzdata">Tzdata</a> package for
    344  1.1  christos the <a href="https://elixir-lang.org">Elixir</a> language downloads
    345  1.1  christos and compiles tz source and exposes <abbr
    346  1.1  christos title="Application Program Interface">API</abbr>s for use. It is
    347  1.1  christos freely available under the <abbr>MIT</abbr> license.</li>
    348  1.1  christos <li>Java-based compilers and libraries include:
    349  1.1  christos <ul>
    350  1.1  christos <li>The <a
    351  1.1  christos href="http://www.oracle.com/technetwork/java/javase/tzupdater-readme-136440.html">TZUpdater
    352  1.1  christos tool</a> compiles <code><abbr>tz</abbr></code> source into the format used by
    353  1.1  christos Oracle Java.</li>
    354  1.1  christos <li>The <a
    355  1.1  christos href="http://www.oracle.com/technetwork/articles/java/jf14-date-time-2125367.html">Java
    356  1.1  christos 8 <code>java.time</code> <abbr>API</abbr></a> can be supplemented by <a
    357  1.1  christos href="http://www.threeten.org/threeten-extra/">ThreeTen-Extra</a>,
    358  1.1  christos which is freely available under a <abbr>BSD</abbr>-style license.</li>
    359  1.1  christos <li><a href="http://www.joda.org/joda-time/">Joda-Time &ndash; Java date
    360  1.1  christos and time <abbr>API</abbr></a> contains a class
    361  1.1  christos <code>org.joda.time.tz.ZoneInfoCompiler</code> that compiles
    362  1.1  christos <code><abbr>tz</abbr></code> source into a binary format. It inspired
    363  1.1  christos Java 8 <code>java.time</code>, which its users should migrate to once
    364  1.1  christos they can assume Java 8 or later. It is available under the <a
    365  1.1  christos href="https://www.apache.org/licenses/LICENSE-2.0">Apache License</a>.</li>
    366  1.1  christos <li><a href="https://github.com/MenoData/Time4J/">Time4J &ndash;
    367  1.1  christos Advanced date, time and interval library for Java</a> contains a class
    368  1.1  christos <code>net.time4j.tool.TimezoneRepositoryCompiler</code> that compiles
    369  1.1  christos <code><abbr>tz</abbr></code> source into a binary format. Time4J is
    370  1.1  christos available under the <a
    371  1.1  christos href="https://www.gnu.org/copyleft/lesser.html"><abbr>GNU</abbr> Lesser
    372  1.1  christos General Public License (<abbr title="Lesser General Public
    373  1.1  christos License">LGPL</abbr>)</a>.</li>
    374  1.1  christos <li><abbr>ICU</abbr> (mentioned <a href="#ICU">above</a>) contains compilers and
    375  1.1  christos Java-based libraries.</li>
    376  1.1  christos </ul>
    377  1.1  christos <li><a href="https://nodatime.org">Noda Time &ndash; Date and
    378  1.1  christos time <abbr>API</abbr> for .NET</a>
    379  1.1  christos and <a href="http://www.babiej.demon.nl/Tz4Net/main.htm">TZ4Net</a>
    380  1.1  christos are similar to Joda-Time and Time4J, but for the .NET framework instead of
    381  1.1  christos Java. They are freely available under the
    382  1.1  christos Apache License
    383  1.1  christos and a <abbr>BSD</abbr>-style license, respectively.</li>
    384  1.1  christos <li><a href="https://en.wikipedia.org/wiki/JavaScript">JavaScript</a>-based
    385  1.1  christos compilers and libraries include:
    386  1.1  christos <ul>
    387  1.1  christos <li><a
    388  1.1  christos href="https://github.com/kshetline/compact-time-zone-generator">CompactTimeZoneGenerator</a>
    389  1.1  christos compiles time zone data into a compact form designed for
    390  1.1  christos JavaScript. It is freely available under a combination of
    391  1.1  christos the <abbr>MIT</abbr> license and the Apache License.</li>
    392  1.1  christos <li><a href="https://momentjs.com/timezone/">Moment Timezone</a> is a
    393  1.1  christos plugin for the <a href="https://momentjs.com">Moment.js</a> date
    394  1.1  christos manipulation library. It is freely available under the <abbr>MIT</abbr>
    395  1.1  christos license.</li>
    396  1.1  christos <li><a href="https://github.com/mde/timezone-js">TimezoneJS.Date</a>'s
    397  1.1  christos <abbr>API</abbr> is upward compatible with standard JavaScript
    398  1.1  christos Dates. It is freely available under the Apache License.</li>
    399  1.1  christos <li><a href="https://github.com/sproutsocial/walltime-js">Walltime-js</a>
    400  1.1  christos translates <abbr>UT</abbr> to local time. It is freely available under
    401  1.1  christos the <abbr>MIT</abbr> license.</li>
    402  1.1  christos </ul>
    403  1.1  christos <li><a href="https://github.com/JuliaTime/">JuliaTime</a> contains a
    404  1.1  christos compiler from <code><abbr>tz</abbr></code> source into
    405  1.1  christos <a href="https://julialang.org/">Julia</a>. It is freely available
    406  1.1  christos under the <abbr>MIT</abbr> license.</li>
    407  1.1  christos <li><a href="http://pytz.sourceforge.net">pytz &ndash; World Timezone
    408  1.1  christos Definitions for Python</a> compiles <code><abbr>tz</abbr></code> source into
    409  1.1  christos <a href="https://www.python.org">Python</a>.
    410  1.1  christos It is freely available under a <abbr>BSD</abbr>-style license.</li>
    411  1.1  christos <li><a href="https://tzinfo.github.io">TZInfo &ndash;
    412  1.1  christos Ruby Timezone Library</a>
    413  1.1  christos compiles <code><abbr>tz</abbr></code> source into
    414  1.1  christos <a href="https://www.ruby-lang.org/en/">Ruby</a>.
    415  1.1  christos It is freely available under the <abbr>MIT</abbr> license.</li>
    416  1.1  christos <li>The <a href="http://www.squeaksource.com/Chronos/">Chronos Date/Time
    417  1.1  christos Library</a> is
    418  1.1  christos a <a href="https://en.wikipedia.org/wiki/Smalltalk">Smalltalk</a> class
    419  1.1  christos library that compiles <code><abbr>tz</abbr></code> source into a time
    420  1.1  christos zone repository whose format
    421  1.1  christos is either proprietary or an <abbr>XML</abbr>-encoded
    422  1.1  christos representation.</li>
    423  1.1  christos <li><a id="Tcl" href="https://tcl.tk">Tcl</a>
    424  1.1  christos contains a developer-oriented parser that compiles <code><abbr>tz</abbr></code>
    425  1.1  christos source into text files, along with a runtime that can read those
    426  1.1  christos files. Tcl is freely available under a <abbr>BSD</abbr>-style
    427  1.1  christos license.</li>
    428  1.1  christos </ul>
    429  1.1  christos <h2 id="binary">Other <code><abbr>tz</abbr></code> binary file readers</h2>
    430  1.1  christos <ul>
    431  1.1  christos <li>The <a
    432  1.1  christos href="https://www.gnu.org/software/libc/"><abbr>GNU</abbr> C
    433  1.1  christos Library</a>
    434  1.1  christos has an independent, thread-safe implementation of
    435  1.1  christos a <code><abbr>tz</abbr></code> binary file reader.
    436  1.1  christos This library is freely available under the LGPL
    437  1.1  christos and is widely used in <abbr>GNU</abbr>/Linux systems.</li>
    438  1.1  christos <li><a href="https://www.gnome.org">GNOME</a>'s
    439  1.1  christos <a href="https://developer.gnome.org/glib/">GLib</a> has
    440  1.1  christos a <code><abbr>tz</abbr></code> binary file reader written in C that
    441  1.1  christos creates a <code>GTimeZone</code> object representing sets
    442  1.1  christos of <abbr>UT</abbr> offsets.
    443  1.1  christos It is freely available under the <abbr>LGPL</abbr>.</li>
    444  1.1  christos <li>The
    445  1.1  christos <a href="https://github.com/bloomberg/bde/wiki">BDE Standard Library</a>'s
    446  1.1  christos <code>baltzo::TimeZoneUtil</code> component contains a C++
    447  1.1  christos implementation of a binary file reader. It is freely available under
    448  1.1  christos the Apache License.</li>
    449  1.1  christos <li><a href="https://github.com/google/cctz">CCTZ</a> is a simple C++
    450  1.1  christos library that translates between <abbr>UT</abbr> and civil time and
    451  1.1  christos can read binary files. It is freely available under the Apache
    452  1.1  christos License.</li>
    453  1.1  christos <li><a href="http://bmsi.com/java/#TZ">ZoneInfo.java</a>
    454  1.1  christos is a <code><abbr>tz</abbr></code> binary file reader written in Java.
    455  1.1  christos It is freely available under the <abbr>LGPL</abbr>.</li>
    456  1.1  christos <li><a href="https://github.com/derickr/timelib">Timelib</a> is a C
    457  1.1  christos library that reads tz binary files and converts
    458  1.1  christos time stamps from one time zone or format to another.
    459  1.1  christos It is used by <a href="https://secure.php.net"><abbr
    460  1.1  christos title="PHP: Hypertext Preprocessor">PHP</abbr></a>,
    461  1.1  christos <a href="https://hhvm.com"><abbr title="HipHop Virtual Machine">HHVM</abbr></a>,
    462  1.1  christos and <a href="https://www.mongodb.com">MongoDB</a>.
    463  1.1  christos It is freely available under the <abbr>MIT</abbr> license.</li>
    464  1.1  christos <li><a href="https://github.com/bigeasy/timezone">Timezone</a> is a
    465  1.1  christos JavaScript library that supports date arithmetic that is time zone
    466  1.1  christos aware. It is freely available under the <abbr>MIT</abbr> license.</li>
    467  1.1  christos <li>Tcl, mentioned <a href="#Tcl">above</a>, also contains a
    468  1.1  christos <code><abbr>tz</abbr></code> binary file reader.</li>
    469  1.1  christos <li><a href="http://search.cpan.org/perldoc?DateTime::TimeZone::Tzfile">
    470  1.1  christos DateTime::TimeZone::Tzfile</a>
    471  1.1  christos is a <code><abbr>tz</abbr></code> binary file reader written in Perl.
    472  1.1  christos It is freely available under the same terms as Perl
    473  1.1  christos (dual <abbr>GPL</abbr> and Artistic license).</li>
    474  1.1  christos <li>The
    475  1.1  christos public-domain <a href="https://github.com/dbaron/tz.js">tz.js</a>
    476  1.1  christos library contains a Python tool that
    477  1.1  christos converts <code><abbr>tz</abbr></code> binary data into
    478  1.1  christos <abbr>JSON</abbr>-format data suitable for use
    479  1.1  christos in its JavaScript library for time zone conversion. Dates before 1970
    480  1.1  christos are not supported.</li>
    481  1.1  christos <li>The <a
    482  1.1  christos href="https://hackage.haskell.org/package/timezone-olson">timezone-olson</a>
    483  1.1  christos package contains <a href="https://www.haskell.org">Haskell</a> code that
    484  1.1  christos parses and uses <code><abbr>tz</abbr></code> binary data. It is freely
    485  1.1  christos available under a <abbr>BSD</abbr>-style license.</li>
    486  1.1  christos </ul>
    487  1.1  christos <h2 id="software">Other <code><abbr>tz</abbr></code>-based time zone software</h2>
    488  1.1  christos <ul>
    489  1.1  christos <li><a href="https://foxclocks.org">FoxClocks</a>
    490  1.1  christos is an extension for <a href="https://www.google.com/chrome/">Google
    491  1.1  christos Chrome</a> and for <a
    492  1.1  christos href="https://developer.mozilla.org/en-US/docs/Mozilla/Tech/Toolkit_API">Mozilla
    493  1.1  christos Toolkit</a> applications like <a
    494  1.1  christos href="https://www.mozilla.org/en-US/firefox/new/">Firefox</a> and <a
    495  1.1  christos href="https://www.mozilla.org/en-US/thunderbird/">Thunderbird</a>.
    496  1.1  christos It displays multiple clocks in the application window, and has a mapping
    497  1.1  christos interface to <a href="https://www.google.com/earth/">Google Earth</a>.
    498  1.1  christos It is freely available under the <abbr>GPL</abbr>.</li>
    499  1.1  christos <li><a href="https://golang.org">Go programming language</a>
    500  1.1  christos implementations contain a copy of a 32-bit subset of a recent
    501  1.1  christos <code><abbr>tz</abbr></code> database in a
    502  1.1  christos Go-specific format.</li>
    503  1.1  christos <li><a
    504  1.1  christos href="http://users.skynet.be/Peter.Verthez/projects/intclock/">International
    505  1.1  christos clock (intclock)</a> is a clock that displays multiple time zones on
    506  1.1  christos <abbr>GNU</abbr>/Linux and similar systems. It is freely available
    507  1.1  christos under the <abbr>GPL</abbr>.</li>
    508  1.1  christos <li>Microsoft Windows 8.1
    509  1.1  christos and later has <code><abbr>tz</abbr></code> data and <abbr>CLDR</abbr>
    510  1.1  christos data (mentioned <a href="#CLDR">below</a>) used by
    511  1.1  christos <a href="https://en.wikipedia.org/wiki/Windows_Runtime">Windows Runtime</a>
    512  1.1  christos classes such as <a
    513  1.1  christos href="https://msdn.microsoft.com/en-us/library/windows/apps/windows.globalization.datetimeformatting.datetimeformatter.aspx"><code>DateTimeFormatter</code></a>.
    514  1.1  christos <a id="System.TimeZoneInfo"
    515  1.1  christos href="https://blogs.msdn.microsoft.com/bclteam/2007/06/07/exploring-windows-time-zones-with-system-timezoneinfo-josh-free/">Exploring
    516  1.1  christos Windows Time Zones with <code>System.TimeZoneInfo</code></a> describes
    517  1.1  christos the older, proprietary method of Microsoft Windows 2000 and later,
    518  1.1  christos which stores time zone data in the
    519  1.1  christos <a href="https://en.wikipedia.org/wiki/Windows_Registry">Windows Registry</a>. The
    520  1.1  christos <a
    521  1.1  christos href="https://unicode.org/cldr/charts/latest/supplemental/zone_tzid.html">Zone &rarr;
    522  1.1  christos Tzid table</a> or <a
    523  1.1  christos href="https://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml"><abbr>XML</abbr>
    524  1.1  christos file</a> of the <abbr>CLDR</abbr> data maps proprietary zone IDs
    525  1.1  christos to <code><abbr>tz</abbr></code> names.
    526  1.1  christos <li><a
    527  1.1  christos href="https://www.oracle.com/java/index.html">Oracle
    528  1.1  christos Java</a> contains a copy of a subset of a recent
    529  1.1  christos <code><abbr>tz</abbr></code> database in a
    530  1.1  christos Java-specific format.</li>
    531  1.1  christos <li><a href="https://www.relativedata.com/time-zone-master">Time Zone
    532  1.1  christos Master</a> is a Microsoft Windows clock program that can automatically
    533  1.1  christos download, compile and use <code>tz</code> releases. The Basic version
    534  1.1  christos is free.</li>
    535  1.1  christos <li><a
    536  1.1  christos href="http://veladg.com/velaterra.html">VelaTerra</a> is
    537  1.1  christos a macOS program. Its developers
    538  1.1  christos <a href="http://veladg.com/tzoffer.html">offer free
    539  1.1  christos licenses</a> to <code><abbr>tz</abbr></code> contributors.</li>
    540  1.1  christos </ul>
    541  1.1  christos <h2 id="other-dbs">Other time zone databases</h2>
    542  1.1  christos <ul>
    543  1.1  christos <li><a href="https://www.astro.com/atlas">Time-zone Atlas</a>
    544  1.1  christos is Astrodienst's Web version of Shanks and Pottenger's
    545  1.1  christos time zone history atlases also published in <a
    546  1.1  christos href="https://astrocom.com/astrology-products/software/acs-atlas-software">software</a>
    547  1.1  christos form by <a href="https://astrocom.com">ACS-Starcrafts</a>.
    548  1.1  christos These atlases are extensive but unreliable, as Shanks appears to have
    549  1.1  christos guessed many <abbr>UT</abbr> offsets and transitions. The atlases cite no
    550  1.1  christos sources and do not indicate which entries are guesswork.</li>
    551  1.1  christos <li><a href="https://en.wikipedia.org/wiki/HP-UX">HP-UX</a> has a database in
    552  1.1  christos its own <code>tztab</code>(4) format.</li>
    553  1.1  christos <li>Microsoft Windows has proprietary data mentioned
    554  1.1  christos <a href="#System.TimeZoneInfo">above</a>.</li>
    555  1.1  christos <li><a href="https://www.worldtimeserver.com">World Time Server</a>
    556  1.1  christos is another time zone database.</li>
    557  1.1  christos <li><a href="http://tycho.usno.navy.mil/tzones.html">World Time Zones</a>
    558  1.1  christos contains data from the Time Service Department of the
    559  1.1  christos <abbr>US</abbr> Naval Observatory.</li>
    560  1.1  christos <li>The <a
    561  1.1  christos href="https://www.iata.org/publications/store/Pages/standard-schedules-information.aspx">Standard
    562  1.1  christos Schedules Information Manual</a> of the
    563  1.1  christos International Air Transport Association
    564  1.1  christos gives current time zone rules for airports served by commercial aviation.</li>
    565  1.1  christos </ul>
    566  1.1  christos <h2 id="maps">Maps</h2>
    567  1.1  christos <ul>
    568  1.1  christos <li>The <a href="https://www.cia.gov/index.html">United States Central
    569  1.1  christos Intelligence Agency (<abbr
    570  1.1  christos title="Central Intelligence Agency">CIA</abbr>)</a> publishes a <a
    571  1.1  christos href="https://www.cia.gov/library/publications/the-world-factbook/graphics/ref_maps/physical/pdf/standard_time_zones_of_the_world.pdf">time
    572  1.1  christos zone map</a>; the
    573  1.1  christos <a
    574  1.1  christos href="https://www.lib.utexas.edu/maps/world.html">Perry&ndash;Casta&ntilde;eda
    575  1.1  christos Library Map Collection</a>
    576  1.1  christos of the University of Texas at Austin has copies of
    577  1.1  christos recent editions.
    578  1.1  christos The pictorial quality is good,
    579  1.1  christos but the maps do not indicate daylight saving time,
    580  1.1  christos and parts of the data are a few years out of date.</li>
    581  1.1  christos <li><a href="https://www.worldtimezone.com">Current time around the world
    582  1.1  christos and standard time zones map of the world</a>
    583  1.1  christos has several fancy time zone maps; it covers Russia particularly well.
    584  1.1  christos The maps' pictorial quality is not quite as good as the
    585  1.1  christos <abbr>CIA</abbr>'s
    586  1.1  christos but the maps are more up to date.</li>
    587  1.1  christos <li><a
    588  1.1  christos href="https://blog.poormansmath.net/how-much-is-time-wrong-around-the-world/">How
    589  1.1  christos much is time wrong around the world?</a> maps the difference between
    590  1.1  christos mean solar and standard time, highlighting areas such as western China
    591  1.1  christos where the two differ greatly. It's a bit out of date, unfortunately.</li>
    592  1.1  christos </ul>
    593  1.1  christos <h2 id="boundaries">Time zone boundaries</h2>
    594  1.1  christos <p>Geographical boundaries between time zone regions are available
    595  1.1  christos from several <a href="https://en.wikipedia.org/wiki/Geolocation">geolocation</a>
    596  1.1  christos services and other sources.</p>
    597  1.1  christos <ul>
    598  1.1  christos <li>Databases of time zone boundaries include:
    599  1.1  christos <ul>
    600  1.1  christos <li><a href="https://github.com/evansiroky/timezone-boundary-builder">Timezone
    601  1.1  christos Boundary Builder</a> extracts
    602  1.1  christos <a href="https://www.openstreetmap.org">Open Street Map</a> data to build
    603  1.1  christos boundaries of <code><abbr>tz</abbr></code> regions.
    604  1.1  christos Its code is freely available under the <abbr>MIT</abbr> license, and
    605  1.1  christos its data entries are freely available under the
    606  1.1  christos <a href="https://opendatacommons.org/licenses/odbl/">Open Data Commons
    607  1.1  christos Open Database License</a>. The maps' borders appear to be quite accurate.</li>
    608  1.1  christos <li><a href="http://efele.net/maps/tz/"><abbr>TZ</abbr> timezones
    609  1.1  christos maps</a> contains <a
    610  1.1  christos href="https://en.wikipedia.org/wiki/Shapefile">shapefiles</a> of
    611  1.1  christos sets of <code><abbr>tz</abbr></code> regions. This includes
    612  1.1  christos <a href="http://efele.net/maps/tz/world/">tz_world</a>, a shapefile
    613  1.1  christos for all the world's regions. These maps are no longer maintained and
    614  1.1  christos are superseded by the Timezone Boundary Builder.</li>
    615  1.1  christos <li><a
    616  1.1  christos href="https://github.com/straup/whereonearth-timezone">Whereonearth-timezone</a>
    617  1.1  christos is in <a href="https://tools.ietf.org/html/rfc7946">GeoJSON</a> format
    618  1.1  christos (Internet <abbr>RFC</abbr> 7946), and combines the
    619  1.1  christos the tz_world shapefiles with the
    620  1.1  christos <a href="https://developer.yahoo.com/geo/geoplanet/">GeoPlanet</a>
    621  1.1  christos dataset.</li>
    622  1.1  christos </ul></li>
    623  1.1  christos <li>Programmatic interfaces that map geographical coordinates via tz_world to
    624  1.1  christos <code><abbr>tz</abbr></code> regions include:
    625  1.1  christos <ul>
    626  1.1  christos <li><a href="https://github.com/mj1856/GeoTimeZone">GeoTimeZone</a> is
    627  1.1  christos written in <a
    628  1.1  christos href="https://en.wikipedia.org/wiki/C_Sharp_(programming_language)">C#</a>
    629  1.1  christos and is freely available under the <abbr>MIT</abbr> license.</li>
    630  1.1  christos <li>The <a href="https://github.com/bradfitz/latlong">latlong package</a>
    631  1.1  christos is written in Go and is freely available under the Apache License.</li>
    632  1.1  christos <li><a href="https://github.com/drtimcooper/LatLongToTimezone">LatLongToTimezone</a>,
    633  1.1  christos in both Java and
    634  1.1  christos <a href="https://en.wikipedia.org/wiki/Swift_(programming_language)">Swift</a>
    635  1.1  christos form, is freely available under the MIT license.</li>
    636  1.1  christos <li>For <a href="https://nodejs.org/en/">Node.js</a>,
    637  1.1  christos the <a href="https://www.npmjs.com/package/geo-tz">geo-tz module</a>
    638  1.1  christos is freely available under the MIT license, and
    639  1.1  christos the <a href="https://www.npmjs.com/package/tz-lookup">tz-lookup module</a>
    640  1.1  christos is in the public domain.</li>
    641  1.1  christos <li>The <a
    642  1.1  christos href="https://github.com/MrMinimal64/timezonefinder">timezonefinder</a>
    643  1.1  christos library for Python is freely available under the MIT license.
    644  1.1  christos <li>The <a
    645  1.1  christos href="https://github.com/gunyarakun/timezone_finder">timezone_finder</a>
    646  1.1  christos library for Ruby is freely available under the MIT license.</li>
    647  1.1  christos <li><a href="https://derickrethans.nl/what-time-is-it.html">What Time
    648  1.1  christos is It Here?</a> applies MongoDB
    649  1.1  christos geospatial query operators to shapefiles' data.</li>
    650  1.1  christos </ul></li>
    651  1.1  christos <li>Free access via a network API, if you register a key, is provided by
    652  1.1  christos the <a href="http://www.geonames.org/export/web-services.html#timezone">GeoNames Timezone web service</a>,
    653  1.1  christos the <a href="https://developers.google.com/maps/documentation/timezone/intro">Google Maps Time Zone API</a>, and
    654  1.1  christos the <a href="https://timezonedb.com">Time Zone Database &amp; API</a>.
    655  1.1  christos Commercial network API access is provided
    656  1.1  christos by <a href="https://askgeo.com">AskGeo</a>
    657  1.1  christos and <a href="https://www.geogarage.com/blog/news-1/post/geogarage-time-zone-api-31">GeoGarage</a>.
    658  1.1  christos </li>
    659  1.1  christos <li>"<a
    660  1.1  christos href="https://stackoverflow.com/questions/16086962/how-to-get-a-time-zone-from-a-location-using-latitude-and-longitude-coordinates/16086964">How
    661  1.1  christos to get a time zone from a location using latitude and longitude
    662  1.1  christos coordinates?</a>" discusses other geolocation possibilities.</li>
    663  1.1  christos <li><a href="http://statoids.com/statoids.html">Administrative
    664  1.1  christos Divisions of Countries ("Statoids")</a> lists
    665  1.1  christos political subdivision data related to time zones.</li>
    666  1.1  christos <li><a href="http://home.kpn.nl/vanadovv/time/Multizones.html">Time
    667  1.1  christos zone boundaries for multizone countries</a> summarizes legal
    668  1.1  christos boundaries between time zones within countries.</li>
    669  1.1  christos <li><a href="http://manifold.net/info/freestuff.shtml">Manifold Software
    670  1.1  christos &ndash; GIS and Database Tools</a> includes a Manifold-format map of
    671  1.1  christos world time zone boundaries distributed under the
    672  1.1  christos <abbr>GPL</abbr>.</li>
    673  1.1  christos <li>A ship within the <a
    674  1.1  christos href="https://en.wikipedia.org/wiki/Territorial_waters">territorial
    675  1.1  christos waters</a> of any nation uses that nation's time. In international
    676  1.1  christos waters, time zone boundaries are meridians 15&deg; apart, except that
    677  1.1  christos <abbr>UT</abbr>&minus;12 and <abbr>UT</abbr>+12 are each 7.5&deg;
    678  1.1  christos wide and are separated by
    679  1.1  christos the 180&deg; meridian (not by the International Date Line, which is
    680  1.1  christos for land and territorial waters only). A captain can change ship's
    681  1.1  christos clocks any time after entering a new time zone; midnight changes are
    682  1.1  christos common.</li>
    683  1.1  christos </ul>
    684  1.1  christos <h2 id="civil">Civil time concepts and history</h2>
    685  1.1  christos <ul>
    686  1.1  christos <li><a href="https://www.nist.gov/pml/time-and-frequency-division/popular-links/walk-through-time">A
    687  1.1  christos Walk through Time</a>
    688  1.1  christos surveys the evolution of timekeeping.</li>
    689  1.1  christos <li><a href="http://www.webexhibits.org/daylightsaving/">About Daylight
    690  1.1  christos Saving Time &ndash; History, rationale, laws &amp; dates</a>
    691  1.1  christos is an overall history of <abbr>DST</abbr>.</li>
    692  1.1  christos <li><a href="https://www.w3.org/TR/timezone/">Working with Time Zones</a>
    693  1.1  christos contains guidelines and best practices for software applications that
    694  1.1  christos deal with civil time.</li>
    695  1.1  christos <li><a href="http://seizethedaylight.com/dst/">A Brief
    696  1.1  christos History of Daylight Saving Time</a> summarizes some of the contentious
    697  1.1  christos history of <abbr>DST</abbr>.</li>
    698  1.1  christos <li><a href="https://www.staff.science.uu.nl/~gent0113/idl/idl.htm">A History of
    699  1.1  christos the International Date Line</a> tells the story of the most important
    700  1.1  christos time zone boundary.</li>
    701  1.1  christos <li><a href="http://statoids.com/tconcept.html">Basic Time
    702  1.1  christos Zone Concepts</a> discusses terminological issues behind time zones.</li>
    703  1.1  christos </ul>
    704  1.1  christos <h2 id="national">National histories of legal time</h2>
    705  1.1  christos <dl>
    706  1.1  christos <dt>Australia</dt>
    707  1.1  christos <dd>The Parliamentary Library has commissioned a <a
    708  1.1  christos href="https://www.aph.gov.au/binaries/library/pubs/rp/2009-10/10rp10.pdf">research
    709  1.1  christos paper on daylight saving time in Australia</a>.
    710  1.1  christos The Bureau of Meteorology publishes a list of <a
    711  1.1  christos href="http://www.bom.gov.au/climate/averages/tables/dst_times.shtml">Implementation
    712  1.1  christos Dates of Daylight Savings Time within Australia</a>.</dd>
    713  1.1  christos <dt>Belgium</dt>
    714  1.1  christos <dd>The Royal Observatory of Belgium maintains a table of <a
    715  1.1  christos href="http://www.astro.oma.be/GENERAL/INFO/nli001a.html"
    716  1.1  christos hreflang="nl">time in Belgium (in Dutch)</a>.</dd>
    717  1.1  christos <dt>Brazil</dt>
    718  1.1  christos <dd>The Time Service Department of the National Observatory
    719  1.1  christos records <a href="http://pcdsh01.on.br/DecHV.html"
    720  1.1  christos hreflang="pt-BR">Brazil's daylight saving time decrees (in
    721  1.1  christos Portuguese)</a>.</dd>
    722  1.1  christos <dt>Canada</dt>
    723  1.1  christos <dd>National Research Council Canada publishes current
    724  1.1  christos and some older information about <a
    725  1.1  christos href="https://www.nrc-cnrc.gc.ca/eng/services/time/time_zones.html">time
    726  1.1  christos zones &amp; daylight saving time</a>.</dd>
    727  1.1  christos <dt>Chile</dt>
    728  1.1  christos <dd>The Hydrographic and Oceanographic Service of the Chilean Navy publishes a
    729  1.1  christos <a href="http://www.horaoficial.cl/historia_hora.html" hreflang="es">history of
    730  1.1  christos Chile's official time (in Spanish)</a>.</dd>
    731  1.1  christos <dt>Czech Republic</dt>
    732  1.1  christos <dd><a href="https://kalendar.beda.cz/kdy-zacina-a-konci-letni-cas"
    733  1.1  christos hreflang="cs">When daylight saving time starts and ends (in Czech)</a>
    734  1.1  christos summarizes and cites historical DST regulations.</dd>
    735  1.1  christos <dt>Germany</dt>
    736  1.1  christos <dd>The National Institute for Science and Technology maintains the <a
    737  1.1  christos href="https://www.ptb.de/cms/en/fachabteilungen/abt4/fb-44/ag-441/realisation-of-legal-time-in-germany.html">Realisation
    738  1.1  christos of Legal Time in Germany</a>.</dd>
    739  1.1  christos <dt>Israel</dt>
    740  1.1  christos <dd>The Interior Ministry periodically issues <a
    741  1.1  christos href="ftp://ftp.cs.huji.ac.il/pub/tz/announcements"
    742  1.1  christos hreflang="he">announcements (in Hebrew)</a>.</dd>
    743  1.1  christos <dt>Italy</dt>
    744  1.1  christos <dd>The National Institute of Metrological Research maintains a
    745  1.1  christos <a href="http://www.nanospin.eu/res/tf/ora_legale_i.shtml">table of civil time
    746  1.1  christos (in Italian)</a>.</dd>
    747  1.1  christos <dt>Mexico</dt>
    748  1.1  christos <dd>The Investigation and Analysis Service of the Mexican Library of
    749  1.1  christos Congress has published a <a
    750  1.1  christos href="http://www.diputados.gob.mx/bibliot/publica/inveyana/polisoc/horver/index.htm"
    751  1.1  christos hreflang="es">history of Mexican local time (in Spanish)</a>.</dd>
    752  1.1  christos <dt>Malaysia</dt>
    753  1.1  christos <dd>See Singapore <a href="#Singapore">below</a>.</dd>
    754  1.1  christos <dt>Netherlands</dt>
    755  1.1  christos <dd><a href="https://www.staff.science.uu.nl/~gent0113/wettijd/wettijd.htm"
    756  1.1  christos hreflang="nl">Legal time in the Netherlands (in Dutch)</a>
    757  1.1  christos covers the history of local time in the Netherlands from ancient times.</dd>
    758  1.1  christos <dt>New Zealand</dt>
    759  1.1  christos <dd>The Department of Internal Affairs maintains a brief <a
    760  1.1  christos href="https://www.dia.govt.nz/Daylight-Saving-History">History of
    761  1.1  christos Daylight Saving</a>. The privately-maintained <a
    762  1.1  christos href="http://astrologyschool.com/nztime.html">History of New Zealand
    763  1.1  christos time</a> has more details.</dd>
    764  1.1  christos <dt>Singapore</dt>
    765  1.1  christos <dd><a id="Singapore"
    766  1.1  christos href="http://www.math.nus.edu.sg/aslaksen/teaching/timezone.html">Why
    767  1.1  christos is Singapore in the "Wrong" Time Zone?</a> details the
    768  1.1  christos history of legal time in Singapore and Malaysia.</dd>
    769  1.1  christos <dt>United Kingdom</dt>
    770  1.1  christos <dd><a
    771  1.1  christos href="https://www.polyomino.org.uk/british-time/">History of
    772  1.1  christos legal time in Britain</a> discusses in detail the country
    773  1.1  christos with perhaps the best-documented history of clock adjustments.
    774  1.1  christos The National Physical Laboratory also maintains an <a
    775  1.1  christos href="http://www.npl.co.uk/educate-explore/what-is-time/archive-of-summer-time-dates">Archive
    776  1.1  christos of Summer time dates</a>.</dd>
    777  1.1  christos <dt>United States</dt>
    778  1.1  christos <dd>The Department of Transportation's <a
    779  1.1  christos href="https://www.transportation.gov/regulations/recent-time-zone-proceedings">Recent
    780  1.1  christos Time Zone Proceedings</a> lists changes to time zone boundaries.</dd>
    781  1.1  christos <dt>Uruguay</dt>
    782  1.1  christos <dd>The Oceanography, Hydrography, and Meteorology Service of the Uruguayan
    783  1.1  christos Navy (SOHMA) publishes an annual <a
    784  1.1  christos href="http://www.armada.mil.uy/Pagina/institucion/dimat/sohma/almanaque.html" hreflang="es">almanac
    785  1.1  christos (in Spanish)</a>.</dd>
    786  1.1  christos </dl>
    787  1.1  christos <h2 id="precision">Precision timekeeping</h2>
    788  1.1  christos <ul>
    789  1.1  christos <li><a
    790  1.1  christos href="http://leapsecond.com/hpan/an1289.pdf">The
    791  1.1  christos Science of Timekeeping</a> is a thorough introduction
    792  1.1  christos to the theory and practice of precision timekeeping.</li>
    793  1.1  christos <li><a href="https://doi.org/10.1007/978-3-319-59909-0">The Science of
    794  1.1  christos Time 2016</a> contains several freely-readable papers.</li>
    795  1.1  christos <li><a href="http://www.ntp.org"><abbr
    796  1.1  christos title="Network Time Protocol">NTP</abbr>: The Network
    797  1.1  christos Time Protocol</a> (Internet <abbr>RFC</abbr> 5905)
    798  1.1  christos discusses how to synchronize clocks of
    799  1.1  christos Internet hosts.</li>
    800  1.1  christos <li>The <a
    801  1.1  christos href="https://www.nist.gov/intelligent-systems-division/ieee-1588">Precision
    802  1.1  christos Time Protocol</a> (<abbr
    803  1.1  christos title="Institute of Electrical and Electronics Engineers">IEEE</abbr> 1588)
    804  1.1  christos can achieve submicrosecond clock accuracy on a local area network.</li>
    805  1.1  christos <li><a
    806  1.1  christos href="https://tools.ietf.org/html/rfc4833">Timezone
    807  1.1  christos Options for <abbr title="Dynamic Host Configuration Protocol">DHCP</abbr></a>
    808  1.1  christos (Internet <abbr>RFC</abbr> 4833)
    809  1.1  christos specifies a <a
    810  1.1  christos href="https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol"><abbr>DHCP</abbr></a>
    811  1.1  christos option for a server to configure
    812  1.1  christos a client's time zone and daylight saving settings automatically.</li>
    813  1.1  christos <li><a
    814  1.1  christos href="https://www.cv.nrao.edu/~rfisher/Ephemerides/times.html">Astronomical
    815  1.1  christos Times</a> explains more abstruse astronomical time scales like
    816  1.1  christos <abbr title="Terrestrial Dynamic Time">TDT</abbr>,
    817  1.1  christos <abbr title="Geocentric Coordinate Time">TCG</abbr>, and
    818  1.1  christos <abbr title="Barycentric Dynamic Time">TDB</abbr>.
    819  1.1  christos <a href="https://www.ucolick.org/~sla/leapsecs/timescales.html">Time
    820  1.1  christos Scales</a> goes into more detail, particularly for historical variants.</li>
    821  1.1  christos <li>The <a href="https://www.iau.org"><abbr
    822  1.1  christos title="International Astronomical Union">IAU</abbr></a>'s <a
    823  1.1  christos href="http://www.iausofa.org"><abbr
    824  1.1  christos title="Standards Of Fundamental Astronomy">SOFA</abbr></a>
    825  1.1  christos collection contains C and <a
    826  1.1  christos href="https://en.wikipedia.org/wiki/Fortran">Fortran</a>
    827  1.1  christos code for converting among time scales like
    828  1.1  christos <abbr title="International Atomic Time">TAI</abbr>,
    829  1.1  christos <abbr>TDB</abbr>, <abbr>TDT</abbr> and
    830  1.1  christos <abbr>UTC</abbr>.</li>
    831  1.1  christos <li><a
    832  1.1  christos href="https://www.giss.nasa.gov/tools/mars24/help/notes.html">Mars24 Sunclock
    833  1.1  christos &ndash; Time on Mars</a> describes Airy Mean Time (<abbr>AMT</abbr>) and the
    834  1.1  christos diverse local time
    835  1.1  christos scales used by each landed mission on Mars.</li>
    836  1.1  christos <li><a href="http://leapsecond.com">LeapSecond.com</a> is
    837  1.1  christos dedicated not only to leap seconds but to precise time and frequency
    838  1.1  christos in general. It covers the state of the art in amateur timekeeping, and
    839  1.1  christos how the art has progressed over the past few decades.</li>
    840  1.1  christos <li><a
    841  1.1  christos href="https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html"><abbr
    842  1.1  christos title="International Earth Rotation and Reference Systems Service">IERS</abbr>
    843  1.1  christos Bulletins</a> contains official publications of the International
    844  1.1  christos Earth Rotation and Reference Systems Service, which decides when leap
    845  1.1  christos seconds occur. The <code>tz</code> code and data support leap seconds
    846  1.1  christos via an optional "<code>right</code>" configuration, as opposed to the
    847  1.1  christos default "<code>posix</code>" configuration.</li>
    848  1.1  christos <li><a href="https://developers.google.com/time/smear">Leap Smear</a>
    849  1.1  christos discusses how to gradually adjust <abbr>POSIX</abbr> clocks near a
    850  1.1  christos leap second so that they disagree with <abbr>UTC</abbr> by at most a
    851  1.1  christos half second, even though every <abbr>POSIX</abbr> minute has exactly
    852  1.1  christos sixty seconds. This approach works with the default <code>tz</code>
    853  1.1  christos "<code>posix</code>" configuration, is <a
    854  1.1  christos href="http://bk1.ntp.org/ntp-stable/README.leapsmear">supported</a> by
    855  1.1  christos the <abbr>NTP</abbr> reference implementation, and is used by major
    856  1.1  christos cloud service providers.</li>
    857  1.1  christos <li>The <a
    858  1.1  christos href="https://pairlist6.pair.net/mailman/listinfo/leapsecs">Leap
    859  1.1  christos Second Discussion List</a> covers <a
    860  1.1  christos href="https://www2.unb.ca/gge/Resources/gpsworld.november99.pdf">McCarthy
    861  1.1  christos and Klepczynski's 1999 proposal to discontinue leap seconds</a>,
    862  1.1  christos discussed further in
    863  1.1  christos <a href="https://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf">The
    864  1.1  christos leap second: its history and possible future</a>.
    865  1.1  christos <a href="https://www.ucolick.org/~sla/leapsecs/"><abbr>UTC</abbr>
    866  1.1  christos might be redefined
    867  1.1  christos without Leap Seconds</a> gives pointers on this
    868  1.1  christos contentious issue, which was active until 2015 and could become active
    869  1.1  christos again.</li>
    870  1.1  christos </ul>
    871  1.1  christos <h2 id="notation">Time notation</h2>
    872  1.1  christos <ul>
    873  1.1  christos <li>The <a id="CLDR" href="http://cldr.unicode.org">Unicode Common Locale Data
    874  1.1  christos Repository (<abbr>CLDR</abbr>) Project</a> has localizations for time
    875  1.1  christos zone names, abbreviations, identifiers, and formats. For example, it
    876  1.1  christos contains French translations for "Eastern European Summer Time",
    877  1.1  christos "<abbr title="Eastern European Summer Time">EEST</abbr>", and
    878  1.1  christos "Bucharest". Its
    879  1.1  christos <a href="https://unicode.org/cldr/charts/latest/by_type/">by-type
    880  1.1  christos charts</a> show these values for many locales. Data values are available in
    881  1.1  christos both <abbr title="Locale Data Markup Language">LDML</abbr>
    882  1.1  christos (an <abbr>XML</abbr> format) and <abbr>JSON</abbr>.
    883  1.1  christos <li>
    884  1.1  christos <a href="https://www.cl.cam.ac.uk/~mgk25/iso-time.html">A summary of
    885  1.1  christos the international standard date and time notation</a> is a good
    886  1.1  christos summary of
    887  1.1  christos <a
    888  1.1  christos href="https://www.iso.org/standard/40874.html"><em><abbr>ISO</abbr>
    889  1.1  christos 8601:2004 &ndash; Data elements and interchange formats &ndash; Information
    890  1.1  christos interchange &ndash; Representation of dates and times</em></a>.</li>
    891  1.1  christos <li>
    892  1.1  christos <a href="https://www.w3.org/TR/xmlschema-2/#dateTime"><abbr>XML</abbr>
    893  1.1  christos Schema: Datatypes &ndash; dateTime</a> specifies a format inspired by
    894  1.1  christos <abbr>ISO</abbr> 8601 that is in common use in <abbr>XML</abbr> data.</li>
    895  1.1  christos <li><a href="https://tools.ietf.org/html/rfc5322#section-3.3">&sect;3.3 of
    896  1.1  christos Internet Message Format</a> (Internet <abbr>RFC</abbr> 5322)
    897  1.1  christos specifies the time notation used in email and <a
    898  1.1  christos href="https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol"><abbr>HTTP</abbr></a>
    899  1.1  christos headers.</li>
    900  1.1  christos <li>
    901  1.1  christos <a href="https://tools.ietf.org/html/rfc3339">Date and Time
    902  1.1  christos on the Internet: Timestamps</a> (Internet <abbr>RFC</abbr> 3339)
    903  1.1  christos specifies an <abbr>ISO</abbr> 8601
    904  1.1  christos profile for use in new Internet
    905  1.1  christos protocols.</li>
    906  1.1  christos <li>
    907  1.1  christos <a href="https://www.hackcraft.net/web/datetime/">Date &amp; Time
    908  1.1  christos Formats on the Web</a> surveys web- and Internet-oriented date and time
    909  1.1  christos formats.</li>
    910  1.1  christos <li>Alphabetic time zone abbreviations should not be used as unique
    911  1.1  christos identifiers for <abbr>UT</abbr> offsets as they are ambiguous in
    912  1.1  christos practice. For example, in English-speaking North America
    913  1.1  christos "<abbr>CST</abbr>" denotes 6 hours behind <abbr>UT</abbr>,
    914  1.1  christos but in China it denotes 8 hours ahead of <abbr>UT</abbr>,
    915  1.1  christos and French-speaking North Americans prefer
    916  1.1  christos "<abbr title="Heure Normale du Centre">HNC</abbr>" to
    917  1.1  christos "<abbr>CST</abbr>". The <code><abbr>tz</abbr></code>
    918  1.1  christos database contains English abbreviations for many time stamps;
    919  1.1  christos unfortunately some of these abbreviations were merely the database maintainers'
    920  1.1  christos inventions, and these have been removed when possible.</li>
    921  1.1  christos <li>Numeric time zone abbreviations typically count hours east of
    922  1.1  christos <abbr>UT</abbr>, e.g., +09 for Japan and
    923  1.1  christos &minus;10 for Hawaii. However, the <abbr>POSIX</abbr>
    924  1.1  christos <code><abbr>TZ</abbr></code> environment variable uses the opposite convention.
    925  1.1  christos For example, one might use <code><abbr>TZ</abbr>="<abbr
    926  1.1  christos title="Japan Standard Time">JST</abbr>-9"</code> and
    927  1.1  christos <code><abbr>TZ</abbr>="<abbr title="Hawaii Standard Time">HST</abbr>10"</code>
    928  1.1  christos for Japan and Hawaii, respectively. If the
    929  1.1  christos <code><abbr>tz</abbr></code> database is available, it is usually better to use
    930  1.1  christos settings like <code><abbr>TZ</abbr>="Asia/Tokyo"</code> and
    931  1.1  christos <code><abbr>TZ</abbr>="Pacific/Honolulu"</code> instead, as this should avoid
    932  1.1  christos confusion, handle old time stamps better, and insulate you better from
    933  1.1  christos any future changes to the rules. One should never set
    934  1.1  christos <abbr>POSIX</abbr> <code><abbr>TZ</abbr></code> to a value like
    935  1.1  christos <code>"GMT-9"</code>, though, since this would incorrectly imply that
    936  1.1  christos local time is nine hours ahead of <abbr>UT</abbr> and the time zone
    937  1.1  christos is called "<abbr>GMT</abbr>".</li>
    938  1.1  christos </ul>
    939  1.1  christos <h2 id="see-also">See also</h2>
    940  1.1  christos <ul>
    941  1.1  christos <li><a href="theory.html">Theory and pragmatics of the tz code and data</a></li>
    942  1.1  christos <li><a href="tz-art.html">Time and the Arts</a></li>
    943  1.1  christos </ul>
    944  1.1  christos <hr>
    945  1.1  christos <address>
    946  1.1  christos This web page is in the public domain, so clarified as of
    947  1.1  christos 2009-05-17 by Arthur David Olson.
    948  1.1  christos <br>
    949  1.1  christos Please send corrections to this web page to the
    950  1.1  christos <a href="mailto:tz (a] iana.org">time zone mailing list</a>.
    951  1.1  christos </address>
    952  1.1  christos </body>
    953  1.1  christos </html>
    954