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4 1.1 christos <title>Sources for time zone and daylight saving time data</title>
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11 1.1 christos <h1>Sources for time zone and daylight saving time data</h1>
12 1.1 christos <p>
13 1.1 christos <a href="https://en.wikipedia.org/wiki/Time_zone">Time zone</a> and
14 1.1 christos <a href="https://en.wikipedia.org/wiki/Daylight_saving_time">daylight-saving</a>
15 1.1 christos rules are controlled by individual
16 1.1 christos governments. They are sometimes changed with little notice, and their
17 1.1 christos histories and planned futures are often recorded only fitfully. Here
18 1.1 christos is a summary of attempts to organize and record relevant data in this
19 1.1 christos area.
20 1.1 christos </p>
21 1.1 christos <h2 id="tzdb">The <code><abbr title="time zone">tz</abbr></code> database</h2>
22 1.1 christos <p>
23 1.1 christos The <a href="https://en.wikipedia.org/wiki/Public_domain">public-domain</a>
24 1.1 christos time zone database contains code and data
25 1.1 christos that represent the history of local time
26 1.1 christos for many representative locations around the globe.
27 1.1 christos It is updated periodically to reflect changes made by political bodies
28 1.1 christos to time zone boundaries and daylight saving rules.
29 1.1 christos This database (known as <code><abbr>tz</abbr></code>,
30 1.1 christos <code><abbr>tzdb</abbr></code>, or <code>zoneinfo</code>)
31 1.1 christos is used by several implementations,
32 1.1 christos including
33 1.1 christos <a href="https://www.gnu.org/software/libc/">the
34 1.1 christos <abbr title="GNU's Not Unix">GNU</abbr>
35 1.1 christos C Library</a> (used in
36 1.1 christos <a href="https://en.wikipedia.org/wiki/Linux"><abbr>GNU</abbr>/Linux</a>),
37 1.1 christos <a href="https://www.android.com">Android</a>,
38 1.1 christos <a href="https://www.freebsd.org">Free<abbr
39 1.1 christos title="Berkeley Software Distribution">BSD</abbr></a>,
40 1.1 christos <a href="https://netbsd.org">Net<abbr>BSD</abbr></a>,
41 1.1 christos <a href="https://www.openbsd.org">Open<abbr>BSD</abbr></a>,
42 1.1 christos <a href="https://www.chromium.org/chromium-os">Chromium OS</a>,
43 1.1 christos <a href="https://cygwin.com">Cygwin</a>,
44 1.1 christos <a href="http://www.delorie.com/djgpp/"><abbr
45 1.1 christos title="DJ's GNU Programming Platform">DJGPP</abbr></a>,
46 1.1 christos <a href="https://en.wikipedia.org/wiki/MINIX">MINIX</a>,
47 1.1 christos <a href="https://www.mysql.com">MySQL</a>,
48 1.1 christos <a href="https://en.wikipedia.org/wiki/WebOS"><abbr
49 1.1 christos title="Web Operating System">webOS</abbr></a>,
50 1.1 christos <a href="https://ibm.com/aix"><abbr
51 1.1 christos title="Advanced Interactive eXecutive">AIX</abbr></a>,
52 1.1 christos <a href="https://en.wikipedia.org/wiki/BlackBerry_10">BlackBerry 10</a>,
53 1.1 christos <a href="https://www.apple.com/ios/"><abbr
54 1.1 christos title="iPhone OS">iOS</abbr></a>,
55 1.1 christos <a href="https://www.apple.com/macos/">macOS</a>,
56 1.1 christos <a href="https://www.microsoft.com/en-us/windows">Microsoft Windows</a>,
57 1.1 christos <a href="https://www.hpe.com/info/openvms">Open<abbr
58 1.1 christos title="Virtual Memory System">VMS</abbr></a>,
59 1.1 christos <a href="https://www.oracle.com/database/index.html">Oracle Database</a>, and
60 1.1 christos <a href="https://www.oracle.com/solaris">Oracle Solaris</a>.</p>
61 1.1 christos <p>
62 1.2 christos Each main entry in the database represents a <dfn>timezone</dfn>
63 1.2 christos for a set of civil-time clocks that have all agreed since 1970.
64 1.2 christos Timezones are typically identified by continent or ocean and then by the
65 1.2 christos name of the largest city within the region containing the clocks.
66 1.1 christos For example, <code>America/New_York</code>
67 1.1 christos represents most of the <abbr title="United States">US</abbr> eastern time zone;
68 1.1 christos <code>America/Phoenix</code> represents most of Arizona, which
69 1.2 christos uses mountain time without daylight saving time (<abbr>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 1.2 christos Associated with each timezone 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 1.2 christos for timestamps 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 1.2 christos <pre><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 1.2 christos <pre><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 1.2 christos <pre><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 1.2 christos machine-readable binary files, one for each location. The binary files
147 1.2 christos are in a special timezone information format (<dfn><abbr>TZif</abbr></dfn>).
148 1.2 christos The code also lets
149 1.2 christos you read a <abbr>TZif</abbr> file and interpret timestamps for that
150 1.1 christos location.</p>
151 1.1 christos <h2 id="changes">Changes to the <code><abbr>tz</abbr></code> database</h2>
152 1.1 christos <p>
153 1.1 christos The <code><abbr>tz</abbr></code> code and data
154 1.1 christos are by no means authoritative. If you find errors, please
155 1.1 christos send changes to <a href="mailto:tz (a] iana.org"><code>tz (a] iana.org</code></a>,
156 1.1 christos the time zone mailing list. You can also <a
157 1.1 christos href="https://mm.icann.org/mailman/listinfo/tz">subscribe</a> to it
158 1.1 christos and browse the <a
159 1.1 christos href="https://mm.icann.org/pipermail/tz/">archive of old
160 1.1 christos messages</a>.</p>
161 1.1 christos <p>
162 1.1 christos If your government plans to change its time zone boundaries or
163 1.1 christos daylight saving rules, inform <code>tz (a] iana.org</code> well in
164 1.1 christos advance, as this will coordinate updates to many cell phones,
165 1.1 christos computers, and other devices around the world. With
166 1.1 christos less than a year's notice there is a good chance that some
167 1.1 christos computer-based clocks will operate incorrectly after the change, due
168 1.1 christos to delays in propagating updates to software and data. The shorter
169 1.1 christos the notice, the more likely clock problems will arise; see "<a
170 1.1 christos href="https://codeofmatt.com/2016/04/23/on-the-timing-of-time-zone-changes/">On
171 1.1 christos the Timing of Time Zone Changes</a>" for examples.
172 1.1 christos </p>
173 1.1 christos <p>
174 1.1 christos Changes to the <code><abbr>tz</abbr></code> code and data are often
175 1.1 christos propagated to clients via operating system updates, so
176 1.1 christos client <code><abbr>tz</abbr></code> data can often be corrected by
177 1.1 christos applying these updates. With GNU/Linux and similar systems, if your
178 1.1 christos maintenance provider has not yet adopted the
179 1.1 christos latest <code><abbr>tz</abbr></code> data, you can often short-circuit
180 1.1 christos the process by tailoring the generic instructions in
181 1.1 christos the <code><abbr>tz</abbr> README</code> file and installing the latest
182 1.1 christos data yourself. System-specific instructions for installing the
183 1.1 christos latest <code><abbr>tz</abbr></code> data have also been published
184 1.1 christos for <a href="https://www.ibm.com/developerworks/aix/library/au-aix-olson-time-zone/index.html"><abbr>AIX</abbr></a>,
185 1.1 christos <a
186 1.1 christos href="https://play.google.com/store/apps/details?id=com.google.android.timezone.data">Android</a>,
187 1.1 christos <a
188 1.1 christos href="http://userguide.icu-project.org/datetime/timezone"><abbr
189 1.1 christos title="International Components for Unicode">ICU</abbr></a>,
190 1.1 christos <a href="https://developer.ibm.com/javasdk/support/dst/jtzu/"><abbr>IBM</abbr></a>
191 1.1 christos and <a
192 1.1 christos href="http://www.oracle.com/technetwork/java/javase/tzupdater-readme-136440.html">Oracle</a>
193 1.1 christos Java, <a href="http://www.joda.org/joda-time/tz_update.html">Joda-Time</a>, <a
194 1.1 christos href="https://dev.mysql.com/doc/refman/en/time-zone-support.html">MySQL</a>,
195 1.1 christos and <a
196 1.1 christos href="https://nodatime.org/userguide/tzdb">Noda Time</a> (see below).
197 1.1 christos </p>
198 1.1 christos <p>Sources for the <code><abbr>tz</abbr></code> database are
199 1.1 christos <a href="https://en.wikipedia.org/wiki/UTF-8"><abbr
200 1.1 christos title="Unicode Transformation Format 8-bit">UTF-8</abbr></a>
201 1.1 christos <a href="https://en.wikipedia.org/wiki/Text_file">text files</a>
202 1.1 christos with lines terminated by <a href="https://en.wikipedia.org/wiki/Newline"><abbr
203 1.1 christos title="linefeed">LF</abbr></a>,
204 1.1 christos which can be modified by common text editors such
205 1.1 christos as <a href="https://www.gnu.org/software/emacs/">GNU Emacs</a>,
206 1.1 christos <a href="https://wiki.gnome.org/Apps/Gedit">gedit</a>, and
207 1.1 christos <a href="https://www.vim.org">vim</a>.
208 1.1 christos Specialized source-file editing can be done via the
209 1.1 christos <a href="https://packagecontrol.io/packages/zoneinfo">Sublime
210 1.1 christos zoneinfo</a> package for <a
211 1.1 christos href="https://www.sublimetext.com">Sublime Text</a> and the <a
212 1.1 christos href="https://marketplace.visualstudio.com/items?itemName=gilmoreorless.vscode-zoneinfo">VSCode
213 1.1 christos zoneinfo</a> extension for <a href="https://code.visualstudio.com">Visual
214 1.1 christos Studio Code</a>.
215 1.1 christos </p>
216 1.1 christos <p>
217 1.1 christos For further information about updates, please see
218 1.1 christos <a href="https://tools.ietf.org/html/rfc6557">Procedures for
219 1.1 christos Maintaining the Time Zone Database</a> (Internet <abbr
220 1.1 christos title="Request For Comments">RFC</abbr> 6557). More detail can be
221 1.1 christos found in <a href="theory.html">Theory and pragmatics of the tz code and data</a>.
222 1.2 christos <a href="https://a0.github.io/a0-tzmigration/">A0 TimeZone Migration</a>
223 1.2 christos displays changes between recent <code><abbr>tzdb</abbr></code> versions.
224 1.1 christos </p>
225 1.1 christos <h2 id="commentary">Commentary on the <code><abbr>tz</abbr></code> database</h2>
226 1.1 christos <ul>
227 1.1 christos <li>The article
228 1.1 christos <a href="https://en.wikipedia.org/wiki/Tz_database">tz database</a> is
229 1.1 christos an encyclopedic summary.</li>
230 1.1 christos <li><a href="tz-how-to.html">How to Read the
231 1.1 christos tz Database Source Files</a> explains the <code><abbr>tz</abbr></code>
232 1.1 christos database format.</li>
233 1.1 christos <li><a
234 1.1 christos href="https://blog.jonudell.net/2009/10/23/a-literary-appreciation-of-the-olsonzoneinfotz-database/">A
235 1.1 christos literary appreciation of the Olson/Zoneinfo/tz database</a> comments on the
236 1.1 christos database's style.</li>
237 1.1 christos </ul>
238 1.1 christos <h2 id="web">Web sites using recent versions of the
239 1.1 christos <code><abbr>tz</abbr></code> database</h2>
240 1.1 christos <p>
241 1.1 christos These are listed roughly in ascending order of complexity and fanciness.
242 1.1 christos </p>
243 1.1 christos <ul>
244 1.1 christos <li><a href="https://time.is">Time.is</a> shows locations'
245 1.1 christos time and zones.</li>
246 1.1 christos <li><a href="https://www.timejones.com">TimeJones.com</a>,
247 1.1 christos <a href="https://timezoneconverterapp.com">Time Zone Converter</a> and
248 1.1 christos <a href="http://worldclock.com">The World Clock</a>
249 1.1 christos are time zone converters.</li>
250 1.1 christos <li><a
251 1.1 christos href="http://twiki.org/cgi-bin/xtra/tzdatepick.html">Date and Time Gateway</a>
252 1.1 christos lets you see the <code><abbr>TZ</abbr></code> values directly.</li>
253 1.1 christos <li><a
254 1.1 christos href="http://www.convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current
255 1.1 christos Time in 1000 Places</a> uses descriptions of the values.</li>
256 1.1 christos <li><a href="http://www.timezoneconverter.com/cgi-bin/tzc.tzc">Time Zone
257 1.1 christos Converter</a>
258 1.1 christos uses a pulldown menu.</li>
259 1.1 christos <li><a href="http://home.kpn.nl/vanadovv/time/TZworld.html">Complete
260 1.1 christos timezone information for all countries</a> displays tables of DST rules.
261 1.1 christos <li><a href="https://www.timeanddate.com/worldclock/">The World Clock –
262 1.1 christos Worldwide</a> lets you sort zone names and convert times.</li>
263 1.1 christos <li><a href="https://24timezones.com">24TimeZones</a> has a world
264 1.1 christos time map and a time converter.</li>
265 1.1 christos <li><a href="https://www.zeitverschiebung.net/en/">Time Difference</a>
266 1.1 christos calculates the current time difference between locations.</li>
267 1.1 christos <li><a href="http://www.wx-now.com">Weather Now</a> and
268 1.1 christos <a href="http://www.thetimenow.com">The Time Now</a> list the weather too.</li>
269 1.1 christos </ul>
270 1.1 christos <h2 id="protocols">Network protocols for <code><abbr>tz</abbr></code> data</h2>
271 1.1 christos <ul>
272 1.1 christos <li>The <a href="https://www.ietf.org">Internet Engineering Task Force</a>'s
273 1.1 christos <a href="https://datatracker.ietf.org/wg/tzdist/charter/">Time Zone Data
274 1.1 christos Distribution Service (tzdist) working group</a> defined <a
275 1.1 christos href="https://tools.ietf.org/html/rfc7808">TZDIST</a>
276 1.1 christos (Internet <abbr>RFC</abbr> 7808), a time zone data distribution service,
277 1.1 christos along with <a href="https://tools.ietf.org/html/rfc7809">CalDAV</a>
278 1.1 christos (Internet <abbr>RFC</abbr> 7809), a calendar access protocol for
279 1.2 christos transferring time zone data by reference.
280 1.2 christos The <a href="https://www.ietf.org/mailman/listinfo/tzdist-bis">tzdist-bis
281 1.2 christos mailing list</a> discusses two Internet drafts: <a
282 1.1 christos id="TZDIST-Geolocate"
283 1.2 christos href="https://tools.ietf.org/html/draft-murchison-tzdist-geolocate">TZDIST
284 1.2 christos Geolocate Extension</a> lets a client determine its timezone
285 1.1 christos from its geographic location using a <a
286 1.2 christos href="https://tools.ietf.org/html/rfc5870">'geo' URI</a>, and
287 1.2 christos <a href="https://tools.ietf.org/html/draft-murchison-tzdist-tzif">The
288 1.2 christos Time Zone Information Format (<abbr>TZif</abbr>)</a> specifies the format of
289 1.2 christos <abbr>TZif</abbr> data.</li>
290 1.1 christos <li>The <a href="https://tools.ietf.org/html/rfc5545">
291 1.1 christos Internet Calendaring and Scheduling Core Object Specification
292 1.1 christos (iCalendar)</a> (Internet <abbr>RFC</abbr> 5445)
293 1.1 christos covers time zone
294 1.1 christos data; see its VTIMEZONE calendar component.
295 1.1 christos The iCalendar format requires specialized parsers and generators; a
296 1.1 christos variant <a href="https://tools.ietf.org/html/rfc6321">xCal</a>
297 1.1 christos (Internet <abbr>RFC</abbr> 6321) uses
298 1.1 christos <a href="https://www.w3.org/XML/"><abbr
299 1.1 christos title="Extensible Markup Language">XML</abbr></a> format, and a variant
300 1.1 christos <a href="https://tools.ietf.org/html/rfc7265">jCal</a>
301 1.1 christos (Internet <abbr>RFC</abbr> 7265)
302 1.1 christos uses <a href="https://www.json.org"><abbr
303 1.1 christos title="JavaScript Object Notation">JSON</abbr></a> format.</li>
304 1.1 christos </ul>
305 1.1 christos <h2 id="compilers">Other <code><abbr>tz</abbr></code> compilers</h2>
306 1.1 christos <ul>
307 1.1 christos <li><a href="https://sourceforge.net/projects/vzic/">Vzic</a> is a <a
308 1.1 christos href="https://en.wikipedia.org/wiki/C_%28programming_language%29">C</a>
309 1.1 christos program that compiles
310 1.1 christos <code><abbr>tz</abbr></code> source into iCalendar-compatible VTIMEZONE files.
311 1.1 christos Vzic is freely
312 1.1 christos available under the <a
313 1.1 christos href="https://www.gnu.org/copyleft/gpl.html"><abbr>GNU</abbr>
314 1.1 christos General Public License (<abbr
315 1.1 christos title="General Public License">GPL</abbr>)</a>.</li>
316 1.1 christos <li><a href="https://sourceforge.net/projects/tzical/">tziCal – tz
317 1.1 christos database conversion utility</a> is like Vzic, except for the <a
318 1.1 christos href="https://www.microsoft.com/net">.NET framework</a>
319 1.1 christos and with a <abbr>BSD</abbr>-style license.</li>
320 1.1 christos <li><a
321 1.1 christos href="http://search.cpan.org/dist/DateTime-TimeZone/">DateTime::TimeZone</a>
322 1.1 christos contains a script <code>parse_olson</code> that compiles
323 1.1 christos <code><abbr>tz</abbr></code> source into <a href="https://www.perl.org">Perl</a>
324 1.1 christos modules. It is part of the Perl <a
325 1.1 christos href="http://datetime.perl.org">DateTime Project</a>, which is freely
326 1.1 christos available under both the <abbr>GPL</abbr> and the Perl Artistic
327 1.1 christos License. DateTime::TimeZone also contains a script
328 1.1 christos <code>tests_from_zdump</code> that generates test cases for each clock
329 1.1 christos transition in the <code><abbr>tz</abbr></code> database.</li>
330 1.1 christos <li>The <a href="https://howardhinnant.github.io/date/tz.html">Time Zone
331 1.1 christos Database Parser</a> is a
332 1.1 christos <a href="https://en.wikipedia.org/wiki/C%2B%2B">C++</a> parser and
333 1.1 christos runtime library that is <a
334 1.1 christos href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0355r4.html">moving
335 1.1 christos forward</a> for inclusion in the next iteration of <a
336 1.1 christos href="https://isocpp.org/std/the-standard"><em><abbr
337 1.1 christos title="International Organization for Standardization">ISO</abbr>
338 1.1 christos International Standard ISO/IEC 14882:2017(E) – Programming
339 1.1 christos Language C++</em></a>.
340 1.1 christos It is freely available under the
341 1.1 christos <abbr title="Massachusetts Institute of Technology">MIT</abbr> license.</li>
342 1.1 christos <li><a id="ICU" href="http://site.icu-project.org">International Components for
343 1.1 christos Unicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a
344 1.1 christos href="https://en.wikipedia.org/wiki/Java_%28programming_language%29">Java</a>
345 1.1 christos libraries for internationalization that
346 1.1 christos has a compiler from <code><abbr>tz</abbr></code> source
347 1.1 christos and from <abbr title="Common Locale Data Repository">CLDR</abbr> data
348 1.1 christos (mentioned <a href="#CLDR">below</a>)
349 1.1 christos into an <abbr>ICU</abbr>-specific format.
350 1.1 christos <abbr>ICU</abbr> is freely available under a
351 1.1 christos <abbr>BSD</abbr>-style license.</li>
352 1.1 christos <li>The <a href="https://github.com/lau/tzdata">Tzdata</a> package for
353 1.1 christos the <a href="https://elixir-lang.org">Elixir</a> language downloads
354 1.1 christos and compiles tz source and exposes <abbr
355 1.1 christos title="Application Program Interface">API</abbr>s for use. It is
356 1.1 christos freely available under the <abbr>MIT</abbr> license.</li>
357 1.1 christos <li>Java-based compilers and libraries include:
358 1.1 christos <ul>
359 1.1 christos <li>The <a
360 1.1 christos href="http://www.oracle.com/technetwork/java/javase/tzupdater-readme-136440.html">TZUpdater
361 1.1 christos tool</a> compiles <code><abbr>tz</abbr></code> source into the format used by
362 1.1 christos Oracle Java.</li>
363 1.1 christos <li>The <a
364 1.1 christos href="http://www.oracle.com/technetwork/articles/java/jf14-date-time-2125367.html">Java
365 1.1 christos 8 <code>java.time</code> <abbr>API</abbr></a> can be supplemented by <a
366 1.1 christos href="http://www.threeten.org/threeten-extra/">ThreeTen-Extra</a>,
367 1.1 christos which is freely available under a <abbr>BSD</abbr>-style license.</li>
368 1.1 christos <li><a href="http://www.joda.org/joda-time/">Joda-Time – Java date
369 1.1 christos and time <abbr>API</abbr></a> contains a class
370 1.1 christos <code>org.joda.time.tz.ZoneInfoCompiler</code> that compiles
371 1.1 christos <code><abbr>tz</abbr></code> source into a binary format. It inspired
372 1.1 christos Java 8 <code>java.time</code>, which its users should migrate to once
373 1.1 christos they can assume Java 8 or later. It is available under the <a
374 1.1 christos href="https://www.apache.org/licenses/LICENSE-2.0">Apache License</a>.</li>
375 1.1 christos <li><a href="https://github.com/MenoData/Time4J/">Time4J –
376 1.1 christos Advanced date, time and interval library for Java</a> contains a class
377 1.1 christos <code>net.time4j.tool.TimezoneRepositoryCompiler</code> that compiles
378 1.1 christos <code><abbr>tz</abbr></code> source into a binary format. Time4J is
379 1.1 christos available under the <a
380 1.1 christos href="https://www.gnu.org/copyleft/lesser.html"><abbr>GNU</abbr> Lesser
381 1.1 christos General Public License (<abbr title="Lesser General Public
382 1.1 christos License">LGPL</abbr>)</a>.</li>
383 1.1 christos <li><abbr>ICU</abbr> (mentioned <a href="#ICU">above</a>) contains compilers and
384 1.1 christos Java-based libraries.</li>
385 1.1 christos </ul>
386 1.1 christos <li><a href="https://nodatime.org">Noda Time – Date and
387 1.1 christos time <abbr>API</abbr> for .NET</a>
388 1.1 christos and <a href="http://www.babiej.demon.nl/Tz4Net/main.htm">TZ4Net</a>
389 1.1 christos are similar to Joda-Time and Time4J, but for the .NET framework instead of
390 1.1 christos Java. They are freely available under the
391 1.1 christos Apache License
392 1.1 christos and a <abbr>BSD</abbr>-style license, respectively.</li>
393 1.1 christos <li><a href="https://en.wikipedia.org/wiki/JavaScript">JavaScript</a>-based
394 1.1 christos compilers and libraries include:
395 1.1 christos <ul>
396 1.1 christos <li><a
397 1.1 christos href="https://github.com/kshetline/compact-time-zone-generator">CompactTimeZoneGenerator</a>
398 1.1 christos compiles time zone data into a compact form designed for
399 1.1 christos JavaScript. It is freely available under a combination of
400 1.1 christos the <abbr>MIT</abbr> license and the Apache License.</li>
401 1.1 christos <li><a href="https://momentjs.com/timezone/">Moment Timezone</a> is a
402 1.1 christos plugin for the <a href="https://momentjs.com">Moment.js</a> date
403 1.1 christos manipulation library. It is freely available under the <abbr>MIT</abbr>
404 1.1 christos license.</li>
405 1.1 christos <li><a href="https://github.com/mde/timezone-js">TimezoneJS.Date</a>'s
406 1.1 christos <abbr>API</abbr> is upward compatible with standard JavaScript
407 1.1 christos Dates. It is freely available under the Apache License.</li>
408 1.1 christos <li><a href="https://github.com/sproutsocial/walltime-js">Walltime-js</a>
409 1.1 christos translates <abbr>UT</abbr> to local time. It is freely available under
410 1.1 christos the <abbr>MIT</abbr> license.</li>
411 1.1 christos </ul>
412 1.1 christos <li><a href="https://github.com/JuliaTime/">JuliaTime</a> contains a
413 1.1 christos compiler from <code><abbr>tz</abbr></code> source into
414 1.1 christos <a href="https://julialang.org/">Julia</a>. It is freely available
415 1.1 christos under the <abbr>MIT</abbr> license.</li>
416 1.2 christos <li><a href="https://github.com/pavkam/tzdb">Delphi/<abbr
417 1.2 christos title="Free Pascal Compiler">FPC</abbr> Time Zone Database</a>
418 1.2 christos compiles from <code><abbr>tz</abbr></code> source into
419 1.2 christos <a href="https://en.wikipedia.org/wiki/Object_Pascal">Object Pascal</a>
420 1.2 christos as compiled by <a href="https://en.wikipedia.org/wiki/Delphi_(IDE)">Delphi</a>
421 1.2 christos and <a
422 1.2 christos href="https://en.wikipedia.org/wiki/Free_Pascal"><abbr>FPC</abbr></a>.
423 1.2 christos It is freely available under a <abbr>BSD</abbr>-style license.</li>
424 1.1 christos <li><a href="http://pytz.sourceforge.net">pytz – World Timezone
425 1.1 christos Definitions for Python</a> compiles <code><abbr>tz</abbr></code> source into
426 1.1 christos <a href="https://www.python.org">Python</a>.
427 1.1 christos It is freely available under a <abbr>BSD</abbr>-style license.</li>
428 1.1 christos <li><a href="https://tzinfo.github.io">TZInfo –
429 1.1 christos Ruby Timezone Library</a>
430 1.1 christos compiles <code><abbr>tz</abbr></code> source into
431 1.1 christos <a href="https://www.ruby-lang.org/en/">Ruby</a>.
432 1.1 christos It is freely available under the <abbr>MIT</abbr> license.</li>
433 1.1 christos <li>The <a href="http://www.squeaksource.com/Chronos/">Chronos Date/Time
434 1.1 christos Library</a> is
435 1.1 christos a <a href="https://en.wikipedia.org/wiki/Smalltalk">Smalltalk</a> class
436 1.1 christos library that compiles <code><abbr>tz</abbr></code> source into a time
437 1.1 christos zone repository whose format
438 1.1 christos is either proprietary or an <abbr>XML</abbr>-encoded
439 1.1 christos representation.</li>
440 1.1 christos <li><a id="Tcl" href="https://tcl.tk">Tcl</a>
441 1.1 christos contains a developer-oriented parser that compiles <code><abbr>tz</abbr></code>
442 1.1 christos source into text files, along with a runtime that can read those
443 1.1 christos files. Tcl is freely available under a <abbr>BSD</abbr>-style
444 1.1 christos license.</li>
445 1.1 christos </ul>
446 1.2 christos <h2 id="TZif">Other <abbr>TZif</abbr> readers</h2>
447 1.1 christos <ul>
448 1.1 christos <li>The <a
449 1.1 christos href="https://www.gnu.org/software/libc/"><abbr>GNU</abbr> C
450 1.1 christos Library</a>
451 1.1 christos has an independent, thread-safe implementation of
452 1.2 christos a <abbr>TZif</abbr> file reader.
453 1.1 christos This library is freely available under the LGPL
454 1.1 christos and is widely used in <abbr>GNU</abbr>/Linux systems.</li>
455 1.1 christos <li><a href="https://www.gnome.org">GNOME</a>'s
456 1.1 christos <a href="https://developer.gnome.org/glib/">GLib</a> has
457 1.2 christos a <abbr>TZif</abbr> file reader written in C that
458 1.1 christos creates a <code>GTimeZone</code> object representing sets
459 1.1 christos of <abbr>UT</abbr> offsets.
460 1.1 christos It is freely available under the <abbr>LGPL</abbr>.</li>
461 1.1 christos <li>The
462 1.1 christos <a href="https://github.com/bloomberg/bde/wiki">BDE Standard Library</a>'s
463 1.1 christos <code>baltzo::TimeZoneUtil</code> component contains a C++
464 1.2 christos implementation of a <abbr>TZif</abbr> file reader. It is freely available under
465 1.1 christos the Apache License.</li>
466 1.1 christos <li><a href="https://github.com/google/cctz">CCTZ</a> is a simple C++
467 1.1 christos library that translates between <abbr>UT</abbr> and civil time and
468 1.2 christos can read <abbr>TZif</abbr> files. It is freely available under the Apache
469 1.1 christos License.</li>
470 1.1 christos <li><a href="http://bmsi.com/java/#TZ">ZoneInfo.java</a>
471 1.2 christos is a <abbr>TZif</abbr> file reader written in Java.
472 1.1 christos It is freely available under the <abbr>LGPL</abbr>.</li>
473 1.1 christos <li><a href="https://github.com/derickr/timelib">Timelib</a> is a C
474 1.2 christos library that reads <abbr>TZif</abbr> files and converts
475 1.2 christos timestamps from one time zone or format to another.
476 1.1 christos It is used by <a href="https://secure.php.net"><abbr
477 1.1 christos title="PHP: Hypertext Preprocessor">PHP</abbr></a>,
478 1.1 christos <a href="https://hhvm.com"><abbr title="HipHop Virtual Machine">HHVM</abbr></a>,
479 1.1 christos and <a href="https://www.mongodb.com">MongoDB</a>.
480 1.1 christos It is freely available under the <abbr>MIT</abbr> license.</li>
481 1.1 christos <li><a href="https://github.com/bigeasy/timezone">Timezone</a> is a
482 1.1 christos JavaScript library that supports date arithmetic that is time zone
483 1.1 christos aware. It is freely available under the <abbr>MIT</abbr> license.</li>
484 1.1 christos <li>Tcl, mentioned <a href="#Tcl">above</a>, also contains a
485 1.2 christos <abbr>TZif</abbr> file reader.</li>
486 1.1 christos <li><a href="http://search.cpan.org/perldoc?DateTime::TimeZone::Tzfile">
487 1.1 christos DateTime::TimeZone::Tzfile</a>
488 1.2 christos is a <abbr>TZif</abbr> file reader written in Perl.
489 1.1 christos It is freely available under the same terms as Perl
490 1.1 christos (dual <abbr>GPL</abbr> and Artistic license).</li>
491 1.1 christos <li>The
492 1.1 christos public-domain <a href="https://github.com/dbaron/tz.js">tz.js</a>
493 1.1 christos library contains a Python tool that
494 1.2 christos converts <abbr>TZif</abbr> data into
495 1.1 christos <abbr>JSON</abbr>-format data suitable for use
496 1.1 christos in its JavaScript library for time zone conversion. Dates before 1970
497 1.1 christos are not supported.</li>
498 1.1 christos <li>The <a
499 1.1 christos href="https://hackage.haskell.org/package/timezone-olson">timezone-olson</a>
500 1.1 christos package contains <a href="https://www.haskell.org">Haskell</a> code that
501 1.2 christos parses and uses <abbr>TZif</abbr> data. It is freely
502 1.1 christos available under a <abbr>BSD</abbr>-style license.</li>
503 1.1 christos </ul>
504 1.1 christos <h2 id="software">Other <code><abbr>tz</abbr></code>-based time zone software</h2>
505 1.1 christos <ul>
506 1.1 christos <li><a href="https://foxclocks.org">FoxClocks</a>
507 1.1 christos is an extension for <a href="https://www.google.com/chrome/">Google
508 1.1 christos Chrome</a> and for <a
509 1.1 christos href="https://developer.mozilla.org/en-US/docs/Mozilla/Tech/Toolkit_API">Mozilla
510 1.1 christos Toolkit</a> applications like <a
511 1.1 christos href="https://www.mozilla.org/en-US/firefox/new/">Firefox</a> and <a
512 1.1 christos href="https://www.mozilla.org/en-US/thunderbird/">Thunderbird</a>.
513 1.1 christos It displays multiple clocks in the application window, and has a mapping
514 1.1 christos interface to <a href="https://www.google.com/earth/">Google Earth</a>.
515 1.1 christos It is freely available under the <abbr>GPL</abbr>.</li>
516 1.1 christos <li><a href="https://golang.org">Go programming language</a>
517 1.1 christos implementations contain a copy of a 32-bit subset of a recent
518 1.1 christos <code><abbr>tz</abbr></code> database in a
519 1.1 christos Go-specific format.</li>
520 1.1 christos <li><a
521 1.1 christos href="http://users.skynet.be/Peter.Verthez/projects/intclock/">International
522 1.1 christos clock (intclock)</a> is a clock that displays multiple time zones on
523 1.1 christos <abbr>GNU</abbr>/Linux and similar systems. It is freely available
524 1.1 christos under the <abbr>GPL</abbr>.</li>
525 1.1 christos <li>Microsoft Windows 8.1
526 1.1 christos and later has <code><abbr>tz</abbr></code> data and <abbr>CLDR</abbr>
527 1.1 christos data (mentioned <a href="#CLDR">below</a>) used by
528 1.1 christos <a href="https://en.wikipedia.org/wiki/Windows_Runtime">Windows Runtime</a>
529 1.1 christos classes such as <a
530 1.1 christos href="https://msdn.microsoft.com/en-us/library/windows/apps/windows.globalization.datetimeformatting.datetimeformatter.aspx"><code>DateTimeFormatter</code></a>.
531 1.1 christos <a id="System.TimeZoneInfo"
532 1.1 christos href="https://blogs.msdn.microsoft.com/bclteam/2007/06/07/exploring-windows-time-zones-with-system-timezoneinfo-josh-free/">Exploring
533 1.1 christos Windows Time Zones with <code>System.TimeZoneInfo</code></a> describes
534 1.1 christos the older, proprietary method of Microsoft Windows 2000 and later,
535 1.1 christos which stores time zone data in the
536 1.1 christos <a href="https://en.wikipedia.org/wiki/Windows_Registry">Windows Registry</a>. The
537 1.1 christos <a
538 1.1 christos href="https://unicode.org/cldr/charts/latest/supplemental/zone_tzid.html">Zone →
539 1.1 christos Tzid table</a> or <a
540 1.1 christos href="https://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml"><abbr>XML</abbr>
541 1.1 christos file</a> of the <abbr>CLDR</abbr> data maps proprietary zone IDs
542 1.1 christos to <code><abbr>tz</abbr></code> names.
543 1.1 christos <li><a
544 1.1 christos href="https://www.oracle.com/java/index.html">Oracle
545 1.1 christos Java</a> contains a copy of a subset of a recent
546 1.1 christos <code><abbr>tz</abbr></code> database in a
547 1.1 christos Java-specific format.</li>
548 1.2 christos <li><a href="https://relativedata.com/page/Time-Zone-Master">Time Zone
549 1.1 christos Master</a> is a Microsoft Windows clock program that can automatically
550 1.1 christos download, compile and use <code>tz</code> releases. The Basic version
551 1.1 christos is free.</li>
552 1.1 christos <li><a
553 1.1 christos href="http://veladg.com/velaterra.html">VelaTerra</a> is
554 1.1 christos a macOS program. Its developers
555 1.1 christos <a href="http://veladg.com/tzoffer.html">offer free
556 1.1 christos licenses</a> to <code><abbr>tz</abbr></code> contributors.</li>
557 1.1 christos </ul>
558 1.1 christos <h2 id="other-dbs">Other time zone databases</h2>
559 1.1 christos <ul>
560 1.1 christos <li><a href="https://www.astro.com/atlas">Time-zone Atlas</a>
561 1.1 christos is Astrodienst's Web version of Shanks and Pottenger's
562 1.1 christos time zone history atlases also published in <a
563 1.1 christos href="https://astrocom.com/astrology-products/software/acs-atlas-software">software</a>
564 1.1 christos form by <a href="https://astrocom.com">ACS-Starcrafts</a>.
565 1.1 christos These atlases are extensive but unreliable, as Shanks appears to have
566 1.1 christos guessed many <abbr>UT</abbr> offsets and transitions. The atlases cite no
567 1.1 christos sources and do not indicate which entries are guesswork.</li>
568 1.1 christos <li><a href="https://en.wikipedia.org/wiki/HP-UX">HP-UX</a> has a database in
569 1.1 christos its own <code>tztab</code>(4) format.</li>
570 1.1 christos <li>Microsoft Windows has proprietary data mentioned
571 1.1 christos <a href="#System.TimeZoneInfo">above</a>.</li>
572 1.1 christos <li><a href="https://www.worldtimeserver.com">World Time Server</a>
573 1.1 christos is another time zone database.</li>
574 1.1 christos <li>The <a
575 1.1 christos href="https://www.iata.org/publications/store/Pages/standard-schedules-information.aspx">Standard
576 1.1 christos Schedules Information Manual</a> of the
577 1.1 christos International Air Transport Association
578 1.1 christos gives current time zone rules for airports served by commercial aviation.</li>
579 1.1 christos </ul>
580 1.1 christos <h2 id="maps">Maps</h2>
581 1.1 christos <ul>
582 1.1 christos <li>The <a href="https://www.cia.gov/index.html">United States Central
583 1.1 christos Intelligence Agency (<abbr
584 1.1 christos title="Central Intelligence Agency">CIA</abbr>)</a> publishes a <a
585 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
586 1.1 christos zone map</a>; the
587 1.1 christos <a
588 1.1 christos href="https://www.lib.utexas.edu/maps/world.html">Perry–Castañeda
589 1.1 christos Library Map Collection</a>
590 1.1 christos of the University of Texas at Austin has copies of
591 1.1 christos recent editions.
592 1.1 christos The pictorial quality is good,
593 1.1 christos but the maps do not indicate daylight saving time,
594 1.1 christos and parts of the data are a few years out of date.</li>
595 1.1 christos <li><a href="https://www.worldtimezone.com">Current time around the world
596 1.1 christos and standard time zones map of the world</a>
597 1.1 christos has several fancy time zone maps; it covers Russia particularly well.
598 1.1 christos The maps' pictorial quality is not quite as good as the
599 1.1 christos <abbr>CIA</abbr>'s
600 1.1 christos but the maps are more up to date.</li>
601 1.1 christos <li><a
602 1.1 christos href="https://blog.poormansmath.net/how-much-is-time-wrong-around-the-world/">How
603 1.1 christos much is time wrong around the world?</a> maps the difference between
604 1.1 christos mean solar and standard time, highlighting areas such as western China
605 1.1 christos where the two differ greatly. It's a bit out of date, unfortunately.</li>
606 1.1 christos </ul>
607 1.1 christos <h2 id="boundaries">Time zone boundaries</h2>
608 1.2 christos <p>Geographical boundaries between timezones are available
609 1.1 christos from several <a href="https://en.wikipedia.org/wiki/Geolocation">geolocation</a>
610 1.1 christos services and other sources.</p>
611 1.1 christos <ul>
612 1.1 christos <li>Databases of time zone boundaries include:
613 1.1 christos <ul>
614 1.1 christos <li><a href="https://github.com/evansiroky/timezone-boundary-builder">Timezone
615 1.1 christos Boundary Builder</a> extracts
616 1.1 christos <a href="https://www.openstreetmap.org">Open Street Map</a> data to build
617 1.2 christos boundaries of <code><abbr>tzdb</abbr></code> timezones.
618 1.1 christos Its code is freely available under the <abbr>MIT</abbr> license, and
619 1.1 christos its data entries are freely available under the
620 1.1 christos <a href="https://opendatacommons.org/licenses/odbl/">Open Data Commons
621 1.1 christos Open Database License</a>. The maps' borders appear to be quite accurate.</li>
622 1.1 christos <li><a href="http://efele.net/maps/tz/"><abbr>TZ</abbr> timezones
623 1.1 christos maps</a> contains <a
624 1.1 christos href="https://en.wikipedia.org/wiki/Shapefile">shapefiles</a> of
625 1.2 christos sets of <code><abbr>tzdb</abbr></code> timezones. This includes
626 1.1 christos <a href="http://efele.net/maps/tz/world/">tz_world</a>, a shapefile
627 1.2 christos for all the world's timezones. These maps are no longer maintained and
628 1.1 christos are superseded by the Timezone Boundary Builder.</li>
629 1.1 christos <li><a
630 1.1 christos href="https://github.com/straup/whereonearth-timezone">Whereonearth-timezone</a>
631 1.1 christos is in <a href="https://tools.ietf.org/html/rfc7946">GeoJSON</a> format
632 1.1 christos (Internet <abbr>RFC</abbr> 7946), and combines the
633 1.1 christos the tz_world shapefiles with the
634 1.1 christos <a href="https://developer.yahoo.com/geo/geoplanet/">GeoPlanet</a>
635 1.1 christos dataset.</li>
636 1.1 christos </ul></li>
637 1.1 christos <li>Programmatic interfaces that map geographical coordinates via tz_world to
638 1.2 christos <code><abbr>tzdb</abbr></code> timezones include:
639 1.1 christos <ul>
640 1.1 christos <li><a href="https://github.com/mj1856/GeoTimeZone">GeoTimeZone</a> is
641 1.1 christos written in <a
642 1.1 christos href="https://en.wikipedia.org/wiki/C_Sharp_(programming_language)">C#</a>
643 1.1 christos and is freely available under the <abbr>MIT</abbr> license.</li>
644 1.1 christos <li>The <a href="https://github.com/bradfitz/latlong">latlong package</a>
645 1.1 christos is written in Go and is freely available under the Apache License.</li>
646 1.1 christos <li><a href="https://github.com/drtimcooper/LatLongToTimezone">LatLongToTimezone</a>,
647 1.1 christos in both Java and
648 1.1 christos <a href="https://en.wikipedia.org/wiki/Swift_(programming_language)">Swift</a>
649 1.1 christos form, is freely available under the MIT license.</li>
650 1.1 christos <li>For <a href="https://nodejs.org/en/">Node.js</a>,
651 1.1 christos the <a href="https://www.npmjs.com/package/geo-tz">geo-tz module</a>
652 1.1 christos is freely available under the MIT license, and
653 1.1 christos the <a href="https://www.npmjs.com/package/tz-lookup">tz-lookup module</a>
654 1.1 christos is in the public domain.</li>
655 1.1 christos <li>The <a
656 1.1 christos href="https://github.com/MrMinimal64/timezonefinder">timezonefinder</a>
657 1.1 christos library for Python is freely available under the MIT license.
658 1.1 christos <li>The <a
659 1.1 christos href="https://github.com/gunyarakun/timezone_finder">timezone_finder</a>
660 1.1 christos library for Ruby is freely available under the MIT license.</li>
661 1.1 christos <li><a href="https://derickrethans.nl/what-time-is-it.html">What Time
662 1.1 christos is It Here?</a> applies MongoDB
663 1.1 christos geospatial query operators to shapefiles' data.</li>
664 1.1 christos </ul></li>
665 1.1 christos <li>Free access via a network API, if you register a key, is provided by
666 1.1 christos the <a href="http://www.geonames.org/export/web-services.html#timezone">GeoNames Timezone web service</a>,
667 1.1 christos the <a href="https://developers.google.com/maps/documentation/timezone/intro">Google Maps Time Zone API</a>, and
668 1.1 christos the <a href="https://timezonedb.com">Time Zone Database & API</a>.
669 1.1 christos Commercial network API access is provided
670 1.1 christos by <a href="https://askgeo.com">AskGeo</a>
671 1.1 christos and <a href="https://www.geogarage.com/blog/news-1/post/geogarage-time-zone-api-31">GeoGarage</a>.
672 1.1 christos </li>
673 1.1 christos <li>"<a
674 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
675 1.1 christos to get a time zone from a location using latitude and longitude
676 1.1 christos coordinates?</a>" discusses other geolocation possibilities.</li>
677 1.1 christos <li><a href="http://statoids.com/statoids.html">Administrative
678 1.1 christos Divisions of Countries ("Statoids")</a> lists
679 1.1 christos political subdivision data related to time zones.</li>
680 1.1 christos <li><a href="http://home.kpn.nl/vanadovv/time/Multizones.html">Time
681 1.1 christos zone boundaries for multizone countries</a> summarizes legal
682 1.1 christos boundaries between time zones within countries.</li>
683 1.1 christos <li><a href="http://manifold.net/info/freestuff.shtml">Manifold Software
684 1.1 christos – GIS and Database Tools</a> includes a Manifold-format map of
685 1.1 christos world time zone boundaries distributed under the
686 1.1 christos <abbr>GPL</abbr>.</li>
687 1.1 christos <li>A ship within the <a
688 1.1 christos href="https://en.wikipedia.org/wiki/Territorial_waters">territorial
689 1.1 christos waters</a> of any nation uses that nation's time. In international
690 1.1 christos waters, time zone boundaries are meridians 15° apart, except that
691 1.1 christos <abbr>UT</abbr>−12 and <abbr>UT</abbr>+12 are each 7.5°
692 1.1 christos wide and are separated by
693 1.1 christos the 180° meridian (not by the International Date Line, which is
694 1.1 christos for land and territorial waters only). A captain can change ship's
695 1.1 christos clocks any time after entering a new time zone; midnight changes are
696 1.1 christos common.</li>
697 1.1 christos </ul>
698 1.1 christos <h2 id="civil">Civil time concepts and history</h2>
699 1.1 christos <ul>
700 1.1 christos <li><a href="https://www.nist.gov/pml/time-and-frequency-division/popular-links/walk-through-time">A
701 1.1 christos Walk through Time</a>
702 1.1 christos surveys the evolution of timekeeping.</li>
703 1.1 christos <li><a href="http://www.webexhibits.org/daylightsaving/">About Daylight
704 1.1 christos Saving Time – History, rationale, laws & dates</a>
705 1.1 christos is an overall history of <abbr>DST</abbr>.</li>
706 1.1 christos <li><a href="https://www.w3.org/TR/timezone/">Working with Time Zones</a>
707 1.1 christos contains guidelines and best practices for software applications that
708 1.1 christos deal with civil time.</li>
709 1.1 christos <li><a href="http://seizethedaylight.com/dst/">A Brief
710 1.1 christos History of Daylight Saving Time</a> summarizes some of the contentious
711 1.1 christos history of <abbr>DST</abbr>.</li>
712 1.1 christos <li><a href="https://www.staff.science.uu.nl/~gent0113/idl/idl.htm">A History of
713 1.1 christos the International Date Line</a> tells the story of the most important
714 1.1 christos time zone boundary.</li>
715 1.1 christos <li><a href="http://statoids.com/tconcept.html">Basic Time
716 1.1 christos Zone Concepts</a> discusses terminological issues behind time zones.</li>
717 1.1 christos </ul>
718 1.1 christos <h2 id="national">National histories of legal time</h2>
719 1.1 christos <dl>
720 1.1 christos <dt>Australia</dt>
721 1.1 christos <dd>The Parliamentary Library has commissioned a <a
722 1.1 christos href="https://www.aph.gov.au/binaries/library/pubs/rp/2009-10/10rp10.pdf">research
723 1.1 christos paper on daylight saving time in Australia</a>.
724 1.1 christos The Bureau of Meteorology publishes a list of <a
725 1.1 christos href="http://www.bom.gov.au/climate/averages/tables/dst_times.shtml">Implementation
726 1.1 christos Dates of Daylight Savings Time within Australia</a>.</dd>
727 1.1 christos <dt>Belgium</dt>
728 1.1 christos <dd>The Royal Observatory of Belgium maintains a table of <a
729 1.1 christos href="http://www.astro.oma.be/GENERAL/INFO/nli001a.html"
730 1.1 christos hreflang="nl">time in Belgium (in Dutch)</a>.</dd>
731 1.1 christos <dt>Brazil</dt>
732 1.1 christos <dd>The Time Service Department of the National Observatory
733 1.1 christos records <a href="http://pcdsh01.on.br/DecHV.html"
734 1.1 christos hreflang="pt-BR">Brazil's daylight saving time decrees (in
735 1.1 christos Portuguese)</a>.</dd>
736 1.1 christos <dt>Canada</dt>
737 1.1 christos <dd>National Research Council Canada publishes current
738 1.1 christos and some older information about <a
739 1.1 christos href="https://www.nrc-cnrc.gc.ca/eng/services/time/time_zones.html">time
740 1.1 christos zones & daylight saving time</a>.</dd>
741 1.1 christos <dt>Chile</dt>
742 1.1 christos <dd>The Hydrographic and Oceanographic Service of the Chilean Navy publishes a
743 1.1 christos <a href="http://www.horaoficial.cl/historia_hora.html" hreflang="es">history of
744 1.1 christos Chile's official time (in Spanish)</a>.</dd>
745 1.1 christos <dt>Czech Republic</dt>
746 1.1 christos <dd><a href="https://kalendar.beda.cz/kdy-zacina-a-konci-letni-cas"
747 1.1 christos hreflang="cs">When daylight saving time starts and ends (in Czech)</a>
748 1.1 christos summarizes and cites historical DST regulations.</dd>
749 1.1 christos <dt>Germany</dt>
750 1.1 christos <dd>The National Institute for Science and Technology maintains the <a
751 1.1 christos href="https://www.ptb.de/cms/en/fachabteilungen/abt4/fb-44/ag-441/realisation-of-legal-time-in-germany.html">Realisation
752 1.1 christos of Legal Time in Germany</a>.</dd>
753 1.1 christos <dt>Israel</dt>
754 1.1 christos <dd>The Interior Ministry periodically issues <a
755 1.1 christos href="ftp://ftp.cs.huji.ac.il/pub/tz/announcements"
756 1.1 christos hreflang="he">announcements (in Hebrew)</a>.</dd>
757 1.1 christos <dt>Italy</dt>
758 1.1 christos <dd>The National Institute of Metrological Research maintains a
759 1.2 christos <a href="http://oldsite.inrim.it/res/tf/ora_legale_i.shtml">table of civil time
760 1.1 christos (in Italian)</a>.</dd>
761 1.2 christos <dt>Macau</dt>
762 1.2 christos <dd>The Meteorological and Geophysical Bureau maintains a
763 1.2 christos <a href="http://www.smg.gov.mo/smg/geophysics/e_t_Summer%20Time.htm">history
764 1.2 christos of summer time</a>. Unfortunately it is incomplete and has errors.</dd>
765 1.2 christos <dt>Malaysia</dt>
766 1.2 christos <dd>See Singapore <a href="#Singapore">below</a>.</dd>
767 1.1 christos <dt>Mexico</dt>
768 1.1 christos <dd>The Investigation and Analysis Service of the Mexican Library of
769 1.1 christos Congress has published a <a
770 1.1 christos href="http://www.diputados.gob.mx/bibliot/publica/inveyana/polisoc/horver/index.htm"
771 1.1 christos hreflang="es">history of Mexican local time (in Spanish)</a>.</dd>
772 1.1 christos <dt>Netherlands</dt>
773 1.1 christos <dd><a href="https://www.staff.science.uu.nl/~gent0113/wettijd/wettijd.htm"
774 1.1 christos hreflang="nl">Legal time in the Netherlands (in Dutch)</a>
775 1.1 christos covers the history of local time in the Netherlands from ancient times.</dd>
776 1.1 christos <dt>New Zealand</dt>
777 1.1 christos <dd>The Department of Internal Affairs maintains a brief <a
778 1.1 christos href="https://www.dia.govt.nz/Daylight-Saving-History">History of
779 1.1 christos Daylight Saving</a>. The privately-maintained <a
780 1.1 christos href="http://astrologyschool.com/nztime.html">History of New Zealand
781 1.1 christos time</a> has more details.</dd>
782 1.1 christos <dt>Singapore</dt>
783 1.1 christos <dd><a id="Singapore"
784 1.1 christos href="http://www.math.nus.edu.sg/aslaksen/teaching/timezone.html">Why
785 1.1 christos is Singapore in the "Wrong" Time Zone?</a> details the
786 1.1 christos history of legal time in Singapore and Malaysia.</dd>
787 1.1 christos <dt>United Kingdom</dt>
788 1.1 christos <dd><a
789 1.1 christos href="https://www.polyomino.org.uk/british-time/">History of
790 1.1 christos legal time in Britain</a> discusses in detail the country
791 1.1 christos with perhaps the best-documented history of clock adjustments.
792 1.1 christos The National Physical Laboratory also maintains an <a
793 1.1 christos href="http://www.npl.co.uk/educate-explore/what-is-time/archive-of-summer-time-dates">Archive
794 1.1 christos of Summer time dates</a>.</dd>
795 1.1 christos <dt>United States</dt>
796 1.1 christos <dd>The Department of Transportation's <a
797 1.1 christos href="https://www.transportation.gov/regulations/recent-time-zone-proceedings">Recent
798 1.1 christos Time Zone Proceedings</a> lists changes to time zone boundaries.</dd>
799 1.1 christos <dt>Uruguay</dt>
800 1.1 christos <dd>The Oceanography, Hydrography, and Meteorology Service of the Uruguayan
801 1.1 christos Navy (SOHMA) publishes an annual <a
802 1.1 christos href="http://www.armada.mil.uy/Pagina/institucion/dimat/sohma/almanaque.html" hreflang="es">almanac
803 1.1 christos (in Spanish)</a>.</dd>
804 1.1 christos </dl>
805 1.1 christos <h2 id="precision">Precision timekeeping</h2>
806 1.1 christos <ul>
807 1.1 christos <li><a
808 1.1 christos href="http://leapsecond.com/hpan/an1289.pdf">The
809 1.1 christos Science of Timekeeping</a> is a thorough introduction
810 1.1 christos to the theory and practice of precision timekeeping.</li>
811 1.1 christos <li><a href="https://doi.org/10.1007/978-3-319-59909-0">The Science of
812 1.1 christos Time 2016</a> contains several freely-readable papers.</li>
813 1.1 christos <li><a href="http://www.ntp.org"><abbr
814 1.1 christos title="Network Time Protocol">NTP</abbr>: The Network
815 1.1 christos Time Protocol</a> (Internet <abbr>RFC</abbr> 5905)
816 1.1 christos discusses how to synchronize clocks of
817 1.1 christos Internet hosts.</li>
818 1.2 christos <li>The <a href="https://www.usenix.org/system/files/conference/nsdi18/nsdi18-geng.pdf"><span style="font-variant: small-caps">Huygens</span></a>
819 1.2 christos family of software algorithms can achieve accuracy to a few tens of
820 1.2 christos nanoseconds in scalable server farms without special hardware.</li>
821 1.1 christos <li>The <a
822 1.1 christos href="https://www.nist.gov/intelligent-systems-division/ieee-1588">Precision
823 1.1 christos Time Protocol</a> (<abbr
824 1.1 christos title="Institute of Electrical and Electronics Engineers">IEEE</abbr> 1588)
825 1.2 christos can achieve submicrosecond clock accuracy on a local area network
826 1.2 christos with special-purpose hardware.</li>
827 1.1 christos <li><a
828 1.1 christos href="https://tools.ietf.org/html/rfc4833">Timezone
829 1.1 christos Options for <abbr title="Dynamic Host Configuration Protocol">DHCP</abbr></a>
830 1.1 christos (Internet <abbr>RFC</abbr> 4833)
831 1.1 christos specifies a <a
832 1.1 christos href="https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol"><abbr>DHCP</abbr></a>
833 1.1 christos option for a server to configure
834 1.1 christos a client's time zone and daylight saving settings automatically.</li>
835 1.1 christos <li><a
836 1.1 christos href="https://www.cv.nrao.edu/~rfisher/Ephemerides/times.html">Astronomical
837 1.1 christos Times</a> explains more abstruse astronomical time scales like
838 1.1 christos <abbr title="Terrestrial Dynamic Time">TDT</abbr>,
839 1.1 christos <abbr title="Geocentric Coordinate Time">TCG</abbr>, and
840 1.1 christos <abbr title="Barycentric Dynamic Time">TDB</abbr>.
841 1.1 christos <a href="https://www.ucolick.org/~sla/leapsecs/timescales.html">Time
842 1.1 christos Scales</a> goes into more detail, particularly for historical variants.</li>
843 1.1 christos <li>The <a href="https://www.iau.org"><abbr
844 1.1 christos title="International Astronomical Union">IAU</abbr></a>'s <a
845 1.1 christos href="http://www.iausofa.org"><abbr
846 1.1 christos title="Standards Of Fundamental Astronomy">SOFA</abbr></a>
847 1.1 christos collection contains C and <a
848 1.1 christos href="https://en.wikipedia.org/wiki/Fortran">Fortran</a>
849 1.1 christos code for converting among time scales like
850 1.1 christos <abbr title="International Atomic Time">TAI</abbr>,
851 1.1 christos <abbr>TDB</abbr>, <abbr>TDT</abbr> and
852 1.1 christos <abbr>UTC</abbr>.</li>
853 1.1 christos <li><a
854 1.1 christos href="https://www.giss.nasa.gov/tools/mars24/help/notes.html">Mars24 Sunclock
855 1.1 christos – Time on Mars</a> describes Airy Mean Time (<abbr>AMT</abbr>) and the
856 1.1 christos diverse local time
857 1.1 christos scales used by each landed mission on Mars.</li>
858 1.1 christos <li><a href="http://leapsecond.com">LeapSecond.com</a> is
859 1.1 christos dedicated not only to leap seconds but to precise time and frequency
860 1.1 christos in general. It covers the state of the art in amateur timekeeping, and
861 1.1 christos how the art has progressed over the past few decades.</li>
862 1.1 christos <li><a
863 1.1 christos href="https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html"><abbr
864 1.1 christos title="International Earth Rotation and Reference Systems Service">IERS</abbr>
865 1.1 christos Bulletins</a> contains official publications of the International
866 1.1 christos Earth Rotation and Reference Systems Service, which decides when leap
867 1.1 christos seconds occur. The <code>tz</code> code and data support leap seconds
868 1.1 christos via an optional "<code>right</code>" configuration, as opposed to the
869 1.1 christos default "<code>posix</code>" configuration.</li>
870 1.1 christos <li><a href="https://developers.google.com/time/smear">Leap Smear</a>
871 1.1 christos discusses how to gradually adjust <abbr>POSIX</abbr> clocks near a
872 1.1 christos leap second so that they disagree with <abbr>UTC</abbr> by at most a
873 1.1 christos half second, even though every <abbr>POSIX</abbr> minute has exactly
874 1.1 christos sixty seconds. This approach works with the default <code>tz</code>
875 1.1 christos "<code>posix</code>" configuration, is <a
876 1.1 christos href="http://bk1.ntp.org/ntp-stable/README.leapsmear">supported</a> by
877 1.1 christos the <abbr>NTP</abbr> reference implementation, and is used by major
878 1.1 christos cloud service providers.</li>
879 1.1 christos <li>The <a
880 1.1 christos href="https://pairlist6.pair.net/mailman/listinfo/leapsecs">Leap
881 1.1 christos Second Discussion List</a> covers <a
882 1.1 christos href="https://www2.unb.ca/gge/Resources/gpsworld.november99.pdf">McCarthy
883 1.1 christos and Klepczynski's 1999 proposal to discontinue leap seconds</a>,
884 1.1 christos discussed further in
885 1.1 christos <a href="https://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf">The
886 1.1 christos leap second: its history and possible future</a>.
887 1.1 christos <a href="https://www.ucolick.org/~sla/leapsecs/"><abbr>UTC</abbr>
888 1.1 christos might be redefined
889 1.1 christos without Leap Seconds</a> gives pointers on this
890 1.1 christos contentious issue, which was active until 2015 and could become active
891 1.1 christos again.</li>
892 1.1 christos </ul>
893 1.1 christos <h2 id="notation">Time notation</h2>
894 1.1 christos <ul>
895 1.1 christos <li>The <a id="CLDR" href="http://cldr.unicode.org">Unicode Common Locale Data
896 1.1 christos Repository (<abbr>CLDR</abbr>) Project</a> has localizations for time
897 1.1 christos zone names, abbreviations, identifiers, and formats. For example, it
898 1.1 christos contains French translations for "Eastern European Summer Time",
899 1.1 christos "<abbr title="Eastern European Summer Time">EEST</abbr>", and
900 1.1 christos "Bucharest". Its
901 1.1 christos <a href="https://unicode.org/cldr/charts/latest/by_type/">by-type
902 1.1 christos charts</a> show these values for many locales. Data values are available in
903 1.1 christos both <abbr title="Locale Data Markup Language">LDML</abbr>
904 1.1 christos (an <abbr>XML</abbr> format) and <abbr>JSON</abbr>.
905 1.1 christos <li>
906 1.1 christos <a href="https://www.cl.cam.ac.uk/~mgk25/iso-time.html">A summary of
907 1.1 christos the international standard date and time notation</a> is a good
908 1.1 christos summary of
909 1.1 christos <a
910 1.1 christos href="https://www.iso.org/standard/40874.html"><em><abbr>ISO</abbr>
911 1.1 christos 8601:2004 – Data elements and interchange formats – Information
912 1.1 christos interchange – Representation of dates and times</em></a>.</li>
913 1.1 christos <li>
914 1.1 christos <a href="https://www.w3.org/TR/xmlschema-2/#dateTime"><abbr>XML</abbr>
915 1.1 christos Schema: Datatypes – dateTime</a> specifies a format inspired by
916 1.1 christos <abbr>ISO</abbr> 8601 that is in common use in <abbr>XML</abbr> data.</li>
917 1.1 christos <li><a href="https://tools.ietf.org/html/rfc5322#section-3.3">§3.3 of
918 1.1 christos Internet Message Format</a> (Internet <abbr>RFC</abbr> 5322)
919 1.1 christos specifies the time notation used in email and <a
920 1.1 christos href="https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol"><abbr>HTTP</abbr></a>
921 1.1 christos headers.</li>
922 1.1 christos <li>
923 1.1 christos <a href="https://tools.ietf.org/html/rfc3339">Date and Time
924 1.1 christos on the Internet: Timestamps</a> (Internet <abbr>RFC</abbr> 3339)
925 1.1 christos specifies an <abbr>ISO</abbr> 8601
926 1.1 christos profile for use in new Internet
927 1.1 christos protocols.</li>
928 1.1 christos <li>
929 1.1 christos <a href="https://www.hackcraft.net/web/datetime/">Date & Time
930 1.1 christos Formats on the Web</a> surveys web- and Internet-oriented date and time
931 1.1 christos formats.</li>
932 1.1 christos <li>Alphabetic time zone abbreviations should not be used as unique
933 1.1 christos identifiers for <abbr>UT</abbr> offsets as they are ambiguous in
934 1.1 christos practice. For example, in English-speaking North America
935 1.1 christos "<abbr>CST</abbr>" denotes 6 hours behind <abbr>UT</abbr>,
936 1.1 christos but in China it denotes 8 hours ahead of <abbr>UT</abbr>,
937 1.1 christos and French-speaking North Americans prefer
938 1.1 christos "<abbr title="Heure Normale du Centre">HNC</abbr>" to
939 1.1 christos "<abbr>CST</abbr>". The <code><abbr>tz</abbr></code>
940 1.2 christos database contains English abbreviations for many timestamps;
941 1.1 christos unfortunately some of these abbreviations were merely the database maintainers'
942 1.1 christos inventions, and these have been removed when possible.</li>
943 1.1 christos <li>Numeric time zone abbreviations typically count hours east of
944 1.1 christos <abbr>UT</abbr>, e.g., +09 for Japan and
945 1.1 christos −10 for Hawaii. However, the <abbr>POSIX</abbr>
946 1.1 christos <code><abbr>TZ</abbr></code> environment variable uses the opposite convention.
947 1.1 christos For example, one might use <code><abbr>TZ</abbr>="<abbr
948 1.1 christos title="Japan Standard Time">JST</abbr>-9"</code> and
949 1.1 christos <code><abbr>TZ</abbr>="<abbr title="Hawaii Standard Time">HST</abbr>10"</code>
950 1.1 christos for Japan and Hawaii, respectively. If the
951 1.1 christos <code><abbr>tz</abbr></code> database is available, it is usually better to use
952 1.1 christos settings like <code><abbr>TZ</abbr>="Asia/Tokyo"</code> and
953 1.1 christos <code><abbr>TZ</abbr>="Pacific/Honolulu"</code> instead, as this should avoid
954 1.2 christos confusion, handle old timestamps better, and insulate you better from
955 1.1 christos any future changes to the rules. One should never set
956 1.1 christos <abbr>POSIX</abbr> <code><abbr>TZ</abbr></code> to a value like
957 1.1 christos <code>"GMT-9"</code>, though, since this would incorrectly imply that
958 1.1 christos local time is nine hours ahead of <abbr>UT</abbr> and the time zone
959 1.1 christos is called "<abbr>GMT</abbr>".</li>
960 1.1 christos </ul>
961 1.1 christos <h2 id="see-also">See also</h2>
962 1.1 christos <ul>
963 1.1 christos <li><a href="theory.html">Theory and pragmatics of the tz code and data</a></li>
964 1.1 christos <li><a href="tz-art.html">Time and the Arts</a></li>
965 1.1 christos </ul>
966 1.1 christos <hr>
967 1.1 christos <address>
968 1.1 christos This web page is in the public domain, so clarified as of
969 1.1 christos 2009-05-17 by Arthur David Olson.
970 1.1 christos <br>
971 1.1 christos Please send corrections to this web page to the
972 1.1 christos <a href="mailto:tz (a] iana.org">time zone mailing list</a>.
973 1.1 christos </address>
974 1.1 christos </body>
975 1.1 christos </html>
976