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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 1.5 christos are in a special timezone information format (<dfn><abbr>TZif</abbr></dfn>)
148 1.5 christos specified by <a href="https://tools.ietf.org/html/8536">Internet
149 1.5 christos <abbr>RFC</abbr> 8536</a>.
150 1.2 christos The code also lets
151 1.2 christos you read a <abbr>TZif</abbr> file and interpret timestamps for that
152 1.1 christos location.</p>
153 1.1 christos <h2 id="changes">Changes to the <code><abbr>tz</abbr></code> database</h2>
154 1.1 christos <p>
155 1.1 christos The <code><abbr>tz</abbr></code> code and data
156 1.1 christos are by no means authoritative. If you find errors, please
157 1.1 christos send changes to <a href="mailto:tz (a] iana.org"><code>tz (a] iana.org</code></a>,
158 1.1 christos the time zone mailing list. You can also <a
159 1.1 christos href="https://mm.icann.org/mailman/listinfo/tz">subscribe</a> to it
160 1.1 christos and browse the <a
161 1.1 christos href="https://mm.icann.org/pipermail/tz/">archive of old
162 1.5 christos messages</a>.
163 1.5 christos <a href="https://tzdata-meta.timtimeonline.com/">Metadata for mailing list
164 1.5 christos discussions</a> and corresponding data changes can be
165 1.5 christos generated <a href="https://github.com/timparenti/tzdata-meta">automatically</a>.
166 1.5 christos </p>
167 1.1 christos <p>
168 1.1 christos If your government plans to change its time zone boundaries or
169 1.1 christos daylight saving rules, inform <code>tz (a] iana.org</code> well in
170 1.1 christos advance, as this will coordinate updates to many cell phones,
171 1.1 christos computers, and other devices around the world. With
172 1.1 christos less than a year's notice there is a good chance that some
173 1.1 christos computer-based clocks will operate incorrectly after the change, due
174 1.1 christos to delays in propagating updates to software and data. The shorter
175 1.1 christos the notice, the more likely clock problems will arise; see "<a
176 1.1 christos href="https://codeofmatt.com/2016/04/23/on-the-timing-of-time-zone-changes/">On
177 1.1 christos the Timing of Time Zone Changes</a>" for examples.
178 1.1 christos </p>
179 1.1 christos <p>
180 1.1 christos Changes to the <code><abbr>tz</abbr></code> code and data are often
181 1.1 christos propagated to clients via operating system updates, so
182 1.1 christos client <code><abbr>tz</abbr></code> data can often be corrected by
183 1.1 christos applying these updates. With GNU/Linux and similar systems, if your
184 1.1 christos maintenance provider has not yet adopted the
185 1.1 christos latest <code><abbr>tz</abbr></code> data, you can often short-circuit
186 1.1 christos the process by tailoring the generic instructions in
187 1.1 christos the <code><abbr>tz</abbr> README</code> file and installing the latest
188 1.1 christos data yourself. System-specific instructions for installing the
189 1.1 christos latest <code><abbr>tz</abbr></code> data have also been published
190 1.1 christos for <a href="https://www.ibm.com/developerworks/aix/library/au-aix-olson-time-zone/index.html"><abbr>AIX</abbr></a>,
191 1.1 christos <a
192 1.1 christos href="https://play.google.com/store/apps/details?id=com.google.android.timezone.data">Android</a>,
193 1.1 christos <a
194 1.1 christos href="http://userguide.icu-project.org/datetime/timezone"><abbr
195 1.1 christos title="International Components for Unicode">ICU</abbr></a>,
196 1.1 christos <a href="https://developer.ibm.com/javasdk/support/dst/jtzu/"><abbr>IBM</abbr></a>
197 1.1 christos and <a
198 1.4 christos href="https://www.oracle.com/technetwork/java/javase/tzupdater-readme-136440.html">Oracle</a>
199 1.4 christos Java, <a href="https://www.joda.org/joda-time/tz_update.html">Joda-Time</a>, <a
200 1.1 christos href="https://dev.mysql.com/doc/refman/en/time-zone-support.html">MySQL</a>,
201 1.1 christos and <a
202 1.1 christos href="https://nodatime.org/userguide/tzdb">Noda Time</a> (see below).
203 1.1 christos </p>
204 1.1 christos <p>Sources for the <code><abbr>tz</abbr></code> database are
205 1.1 christos <a href="https://en.wikipedia.org/wiki/UTF-8"><abbr
206 1.1 christos title="Unicode Transformation Format 8-bit">UTF-8</abbr></a>
207 1.1 christos <a href="https://en.wikipedia.org/wiki/Text_file">text files</a>
208 1.1 christos with lines terminated by <a href="https://en.wikipedia.org/wiki/Newline"><abbr
209 1.1 christos title="linefeed">LF</abbr></a>,
210 1.1 christos which can be modified by common text editors such
211 1.1 christos as <a href="https://www.gnu.org/software/emacs/">GNU Emacs</a>,
212 1.1 christos <a href="https://wiki.gnome.org/Apps/Gedit">gedit</a>, and
213 1.1 christos <a href="https://www.vim.org">vim</a>.
214 1.1 christos Specialized source-file editing can be done via the
215 1.1 christos <a href="https://packagecontrol.io/packages/zoneinfo">Sublime
216 1.1 christos zoneinfo</a> package for <a
217 1.1 christos href="https://www.sublimetext.com">Sublime Text</a> and the <a
218 1.1 christos href="https://marketplace.visualstudio.com/items?itemName=gilmoreorless.vscode-zoneinfo">VSCode
219 1.1 christos zoneinfo</a> extension for <a href="https://code.visualstudio.com">Visual
220 1.1 christos Studio Code</a>.
221 1.1 christos </p>
222 1.1 christos <p>
223 1.1 christos For further information about updates, please see
224 1.1 christos <a href="https://tools.ietf.org/html/rfc6557">Procedures for
225 1.1 christos Maintaining the Time Zone Database</a> (Internet <abbr
226 1.1 christos title="Request For Comments">RFC</abbr> 6557). More detail can be
227 1.1 christos found in <a href="theory.html">Theory and pragmatics of the tz code and data</a>.
228 1.2 christos <a href="https://a0.github.io/a0-tzmigration/">A0 TimeZone Migration</a>
229 1.2 christos displays changes between recent <code><abbr>tzdb</abbr></code> versions.
230 1.1 christos </p>
231 1.1 christos <h2 id="commentary">Commentary on the <code><abbr>tz</abbr></code> database</h2>
232 1.1 christos <ul>
233 1.1 christos <li>The article
234 1.1 christos <a href="https://en.wikipedia.org/wiki/Tz_database">tz database</a> is
235 1.1 christos an encyclopedic summary.</li>
236 1.1 christos <li><a href="tz-how-to.html">How to Read the
237 1.1 christos tz Database Source Files</a> explains the <code><abbr>tz</abbr></code>
238 1.1 christos database format.</li>
239 1.1 christos <li><a
240 1.1 christos href="https://blog.jonudell.net/2009/10/23/a-literary-appreciation-of-the-olsonzoneinfotz-database/">A
241 1.1 christos literary appreciation of the Olson/Zoneinfo/tz database</a> comments on the
242 1.1 christos database's style.</li>
243 1.1 christos </ul>
244 1.1 christos <h2 id="web">Web sites using recent versions of the
245 1.1 christos <code><abbr>tz</abbr></code> database</h2>
246 1.1 christos <p>
247 1.1 christos These are listed roughly in ascending order of complexity and fanciness.
248 1.1 christos </p>
249 1.1 christos <ul>
250 1.1 christos <li><a href="https://time.is">Time.is</a> shows locations'
251 1.1 christos time and zones.</li>
252 1.1 christos <li><a href="https://www.timejones.com">TimeJones.com</a>,
253 1.1 christos <a href="https://timezoneconverterapp.com">Time Zone Converter</a> and
254 1.1 christos <a href="http://worldclock.com">The World Clock</a>
255 1.1 christos are time zone converters.</li>
256 1.1 christos <li><a
257 1.1 christos href="http://twiki.org/cgi-bin/xtra/tzdatepick.html">Date and Time Gateway</a>
258 1.1 christos lets you see the <code><abbr>TZ</abbr></code> values directly.</li>
259 1.1 christos <li><a
260 1.1 christos href="http://www.convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current
261 1.1 christos Time in 1000 Places</a> uses descriptions of the values.</li>
262 1.1 christos <li><a href="http://www.timezoneconverter.com/cgi-bin/tzc.tzc">Time Zone
263 1.1 christos Converter</a>
264 1.1 christos uses a pulldown menu.</li>
265 1.1 christos <li><a href="http://home.kpn.nl/vanadovv/time/TZworld.html">Complete
266 1.1 christos timezone information for all countries</a> displays tables of DST rules.
267 1.1 christos <li><a href="https://www.timeanddate.com/worldclock/">The World Clock –
268 1.1 christos Worldwide</a> lets you sort zone names and convert times.</li>
269 1.1 christos <li><a href="https://24timezones.com">24TimeZones</a> has a world
270 1.1 christos time map and a time converter.</li>
271 1.1 christos <li><a href="https://www.zeitverschiebung.net/en/">Time Difference</a>
272 1.1 christos calculates the current time difference between locations.</li>
273 1.1 christos <li><a href="http://www.wx-now.com">Weather Now</a> and
274 1.1 christos <a href="http://www.thetimenow.com">The Time Now</a> list the weather too.</li>
275 1.1 christos </ul>
276 1.1 christos <h2 id="protocols">Network protocols for <code><abbr>tz</abbr></code> data</h2>
277 1.1 christos <ul>
278 1.1 christos <li>The <a href="https://www.ietf.org">Internet Engineering Task Force</a>'s
279 1.1 christos <a href="https://datatracker.ietf.org/wg/tzdist/charter/">Time Zone Data
280 1.1 christos Distribution Service (tzdist) working group</a> defined <a
281 1.1 christos href="https://tools.ietf.org/html/rfc7808">TZDIST</a>
282 1.1 christos (Internet <abbr>RFC</abbr> 7808), a time zone data distribution service,
283 1.1 christos along with <a href="https://tools.ietf.org/html/rfc7809">CalDAV</a>
284 1.1 christos (Internet <abbr>RFC</abbr> 7809), a calendar access protocol for
285 1.2 christos transferring time zone data by reference.
286 1.2 christos The <a href="https://www.ietf.org/mailman/listinfo/tzdist-bis">tzdist-bis
287 1.5 christos mailing list</a> discusses the Internet draft <a
288 1.1 christos id="TZDIST-Geolocate"
289 1.2 christos href="https://tools.ietf.org/html/draft-murchison-tzdist-geolocate">TZDIST
290 1.5 christos Geolocate Extension</a>, which lets a client determine its timezone
291 1.1 christos from its geographic location using a <a
292 1.5 christos href="https://tools.ietf.org/html/rfc5870">'geo' URI</a>.</li>
293 1.1 christos <li>The <a href="https://tools.ietf.org/html/rfc5545">
294 1.1 christos Internet Calendaring and Scheduling Core Object Specification
295 1.1 christos (iCalendar)</a> (Internet <abbr>RFC</abbr> 5445)
296 1.1 christos covers time zone
297 1.1 christos data; see its VTIMEZONE calendar component.
298 1.1 christos The iCalendar format requires specialized parsers and generators; a
299 1.1 christos variant <a href="https://tools.ietf.org/html/rfc6321">xCal</a>
300 1.1 christos (Internet <abbr>RFC</abbr> 6321) uses
301 1.1 christos <a href="https://www.w3.org/XML/"><abbr
302 1.1 christos title="Extensible Markup Language">XML</abbr></a> format, and a variant
303 1.1 christos <a href="https://tools.ietf.org/html/rfc7265">jCal</a>
304 1.1 christos (Internet <abbr>RFC</abbr> 7265)
305 1.1 christos uses <a href="https://www.json.org"><abbr
306 1.1 christos title="JavaScript Object Notation">JSON</abbr></a> format.</li>
307 1.1 christos </ul>
308 1.1 christos <h2 id="compilers">Other <code><abbr>tz</abbr></code> compilers</h2>
309 1.1 christos <ul>
310 1.1 christos <li><a href="https://sourceforge.net/projects/vzic/">Vzic</a> is a <a
311 1.1 christos href="https://en.wikipedia.org/wiki/C_%28programming_language%29">C</a>
312 1.1 christos program that compiles
313 1.1 christos <code><abbr>tz</abbr></code> source into iCalendar-compatible VTIMEZONE files.
314 1.1 christos Vzic is freely
315 1.1 christos available under the <a
316 1.1 christos href="https://www.gnu.org/copyleft/gpl.html"><abbr>GNU</abbr>
317 1.1 christos General Public License (<abbr
318 1.1 christos title="General Public License">GPL</abbr>)</a>.</li>
319 1.1 christos <li><a href="https://sourceforge.net/projects/tzical/">tziCal – tz
320 1.1 christos database conversion utility</a> is like Vzic, except for the <a
321 1.1 christos href="https://www.microsoft.com/net">.NET framework</a>
322 1.1 christos and with a <abbr>BSD</abbr>-style license.</li>
323 1.1 christos <li><a
324 1.4 christos href="https://metacpan.org/release/DateTime-TimeZone">DateTime::TimeZone</a>
325 1.1 christos contains a script <code>parse_olson</code> that compiles
326 1.1 christos <code><abbr>tz</abbr></code> source into <a href="https://www.perl.org">Perl</a>
327 1.1 christos modules. It is part of the Perl <a
328 1.4 christos href="https://github.com/houseabsolute/DateTime.pm/wiki">DateTime Project</a>,
329 1.4 christos which is freely
330 1.1 christos available under both the <abbr>GPL</abbr> and the Perl Artistic
331 1.1 christos License. DateTime::TimeZone also contains a script
332 1.1 christos <code>tests_from_zdump</code> that generates test cases for each clock
333 1.1 christos transition in the <code><abbr>tz</abbr></code> database.</li>
334 1.1 christos <li>The <a href="https://howardhinnant.github.io/date/tz.html">Time Zone
335 1.1 christos Database Parser</a> is a
336 1.1 christos <a href="https://en.wikipedia.org/wiki/C%2B%2B">C++</a> parser and
337 1.1 christos runtime library that is <a
338 1.1 christos href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0355r4.html">moving
339 1.1 christos forward</a> for inclusion in the next iteration of <a
340 1.1 christos href="https://isocpp.org/std/the-standard"><em><abbr
341 1.1 christos title="International Organization for Standardization">ISO</abbr>
342 1.1 christos International Standard ISO/IEC 14882:2017(E) – Programming
343 1.1 christos Language C++</em></a>.
344 1.1 christos It is freely available under the
345 1.1 christos <abbr title="Massachusetts Institute of Technology">MIT</abbr> license.</li>
346 1.1 christos <li><a id="ICU" href="http://site.icu-project.org">International Components for
347 1.1 christos Unicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a
348 1.1 christos href="https://en.wikipedia.org/wiki/Java_%28programming_language%29">Java</a>
349 1.1 christos libraries for internationalization that
350 1.1 christos has a compiler from <code><abbr>tz</abbr></code> source
351 1.1 christos and from <abbr title="Common Locale Data Repository">CLDR</abbr> data
352 1.1 christos (mentioned <a href="#CLDR">below</a>)
353 1.1 christos into an <abbr>ICU</abbr>-specific format.
354 1.1 christos <abbr>ICU</abbr> is freely available under a
355 1.1 christos <abbr>BSD</abbr>-style license.</li>
356 1.1 christos <li>The <a href="https://github.com/lau/tzdata">Tzdata</a> package for
357 1.1 christos the <a href="https://elixir-lang.org">Elixir</a> language downloads
358 1.1 christos and compiles tz source and exposes <abbr
359 1.1 christos title="Application Program Interface">API</abbr>s for use. It is
360 1.1 christos freely available under the <abbr>MIT</abbr> license.</li>
361 1.1 christos <li>Java-based compilers and libraries include:
362 1.1 christos <ul>
363 1.1 christos <li>The <a
364 1.4 christos href="https://www.oracle.com/technetwork/java/javase/tzupdater-readme-136440.html">TZUpdater
365 1.1 christos tool</a> compiles <code><abbr>tz</abbr></code> source into the format used by
366 1.1 christos Oracle Java.</li>
367 1.1 christos <li>The <a
368 1.4 christos href="https://www.oracle.com/technetwork/articles/java/jf14-date-time-2125367.html">Java
369 1.4 christos SE <code>java.time</code> <abbr>API</abbr></a> in Java 8 and later
370 1.4 christos can be supplemented by <a
371 1.4 christos href="https://www.threeten.org/threeten-extra/">ThreeTen-Extra</a>,
372 1.1 christos which is freely available under a <abbr>BSD</abbr>-style license.</li>
373 1.4 christos <li><a href="https://www.joda.org/joda-time/">Joda-Time – Java date
374 1.1 christos and time <abbr>API</abbr></a> contains a class
375 1.1 christos <code>org.joda.time.tz.ZoneInfoCompiler</code> that compiles
376 1.1 christos <code><abbr>tz</abbr></code> source into a binary format. It inspired
377 1.1 christos Java 8 <code>java.time</code>, which its users should migrate to once
378 1.1 christos they can assume Java 8 or later. It is available under the <a
379 1.1 christos href="https://www.apache.org/licenses/LICENSE-2.0">Apache License</a>.</li>
380 1.4 christos <li><a href="https://github.com/MenoData/Time4A">Time4A: Advanced date and
381 1.4 christos time library for Android</a> and
382 1.4 christos <a href="https://github.com/MenoData/Time4J/">Time4J: Advanced date,
383 1.4 christos time and interval library for Java</a> compile
384 1.4 christos <code><abbr>tz</abbr></code> source into a binary format.
385 1.4 christos Time4A is available under the Apache License and Time4J is
386 1.1 christos available under the <a
387 1.1 christos href="https://www.gnu.org/copyleft/lesser.html"><abbr>GNU</abbr> Lesser
388 1.1 christos General Public License (<abbr title="Lesser General Public
389 1.1 christos License">LGPL</abbr>)</a>.</li>
390 1.1 christos <li><abbr>ICU</abbr> (mentioned <a href="#ICU">above</a>) contains compilers and
391 1.1 christos Java-based libraries.</li>
392 1.1 christos </ul>
393 1.1 christos <li><a href="https://nodatime.org">Noda Time – Date and
394 1.1 christos time <abbr>API</abbr> for .NET</a>
395 1.4 christos is like Joda-Time and Time4J, but for the .NET framework instead of Java.
396 1.4 christos It is freely available under the Apache License.</li>
397 1.1 christos <li><a href="https://en.wikipedia.org/wiki/JavaScript">JavaScript</a>-based
398 1.1 christos compilers and libraries include:
399 1.1 christos <ul>
400 1.1 christos <li><a
401 1.1 christos href="https://github.com/kshetline/compact-time-zone-generator">CompactTimeZoneGenerator</a>
402 1.1 christos compiles time zone data into a compact form designed for
403 1.1 christos JavaScript. It is freely available under a combination of
404 1.1 christos the <abbr>MIT</abbr> license and the Apache License.</li>
405 1.1 christos <li><a href="https://momentjs.com/timezone/">Moment Timezone</a> is a
406 1.1 christos plugin for the <a href="https://momentjs.com">Moment.js</a> date
407 1.1 christos manipulation library. It is freely available under the <abbr>MIT</abbr>
408 1.1 christos license.</li>
409 1.1 christos <li><a href="https://github.com/mde/timezone-js">TimezoneJS.Date</a>'s
410 1.1 christos <abbr>API</abbr> is upward compatible with standard JavaScript
411 1.1 christos Dates. It is freely available under the Apache License.</li>
412 1.1 christos <li><a href="https://github.com/sproutsocial/walltime-js">Walltime-js</a>
413 1.1 christos translates <abbr>UT</abbr> to local time. It is freely available under
414 1.1 christos the <abbr>MIT</abbr> license.</li>
415 1.1 christos </ul>
416 1.1 christos <li><a href="https://github.com/JuliaTime/">JuliaTime</a> contains a
417 1.1 christos compiler from <code><abbr>tz</abbr></code> source into
418 1.1 christos <a href="https://julialang.org/">Julia</a>. It is freely available
419 1.1 christos under the <abbr>MIT</abbr> license.</li>
420 1.2 christos <li><a href="https://github.com/pavkam/tzdb">Delphi/<abbr
421 1.2 christos title="Free Pascal Compiler">FPC</abbr> Time Zone Database</a>
422 1.2 christos compiles from <code><abbr>tz</abbr></code> source into
423 1.2 christos <a href="https://en.wikipedia.org/wiki/Object_Pascal">Object Pascal</a>
424 1.2 christos as compiled by <a href="https://en.wikipedia.org/wiki/Delphi_(IDE)">Delphi</a>
425 1.2 christos and <a
426 1.2 christos href="https://en.wikipedia.org/wiki/Free_Pascal"><abbr>FPC</abbr></a>.
427 1.2 christos It is freely available under a <abbr>BSD</abbr>-style license.</li>
428 1.1 christos <li><a href="http://pytz.sourceforge.net">pytz – World Timezone
429 1.1 christos Definitions for Python</a> compiles <code><abbr>tz</abbr></code> source into
430 1.1 christos <a href="https://www.python.org">Python</a>.
431 1.1 christos It is freely available under a <abbr>BSD</abbr>-style license.</li>
432 1.1 christos <li><a href="https://tzinfo.github.io">TZInfo –
433 1.1 christos Ruby Timezone Library</a>
434 1.1 christos compiles <code><abbr>tz</abbr></code> source into
435 1.1 christos <a href="https://www.ruby-lang.org/en/">Ruby</a>.
436 1.1 christos It is freely available under the <abbr>MIT</abbr> license.</li>
437 1.1 christos <li>The <a href="http://www.squeaksource.com/Chronos/">Chronos Date/Time
438 1.1 christos Library</a> is
439 1.1 christos a <a href="https://en.wikipedia.org/wiki/Smalltalk">Smalltalk</a> class
440 1.1 christos library that compiles <code><abbr>tz</abbr></code> source into a time
441 1.1 christos zone repository whose format
442 1.1 christos is either proprietary or an <abbr>XML</abbr>-encoded
443 1.1 christos representation.</li>
444 1.1 christos <li><a id="Tcl" href="https://tcl.tk">Tcl</a>
445 1.1 christos contains a developer-oriented parser that compiles <code><abbr>tz</abbr></code>
446 1.1 christos source into text files, along with a runtime that can read those
447 1.1 christos files. Tcl is freely available under a <abbr>BSD</abbr>-style
448 1.1 christos license.</li>
449 1.1 christos </ul>
450 1.2 christos <h2 id="TZif">Other <abbr>TZif</abbr> readers</h2>
451 1.1 christos <ul>
452 1.1 christos <li>The <a
453 1.1 christos href="https://www.gnu.org/software/libc/"><abbr>GNU</abbr> C
454 1.1 christos Library</a>
455 1.1 christos has an independent, thread-safe implementation of
456 1.2 christos a <abbr>TZif</abbr> file reader.
457 1.1 christos This library is freely available under the LGPL
458 1.1 christos and is widely used in <abbr>GNU</abbr>/Linux systems.</li>
459 1.1 christos <li><a href="https://www.gnome.org">GNOME</a>'s
460 1.1 christos <a href="https://developer.gnome.org/glib/">GLib</a> has
461 1.2 christos a <abbr>TZif</abbr> file reader written in C that
462 1.1 christos creates a <code>GTimeZone</code> object representing sets
463 1.1 christos of <abbr>UT</abbr> offsets.
464 1.1 christos It is freely available under the <abbr>LGPL</abbr>.</li>
465 1.1 christos <li>The
466 1.1 christos <a href="https://github.com/bloomberg/bde/wiki">BDE Standard Library</a>'s
467 1.1 christos <code>baltzo::TimeZoneUtil</code> component contains a C++
468 1.2 christos implementation of a <abbr>TZif</abbr> file reader. It is freely available under
469 1.1 christos the Apache License.</li>
470 1.1 christos <li><a href="https://github.com/google/cctz">CCTZ</a> is a simple C++
471 1.1 christos library that translates between <abbr>UT</abbr> and civil time and
472 1.2 christos can read <abbr>TZif</abbr> files. It is freely available under the Apache
473 1.1 christos License.</li>
474 1.1 christos <li><a href="http://bmsi.com/java/#TZ">ZoneInfo.java</a>
475 1.2 christos is a <abbr>TZif</abbr> file reader written in Java.
476 1.1 christos It is freely available under the <abbr>LGPL</abbr>.</li>
477 1.1 christos <li><a href="https://github.com/derickr/timelib">Timelib</a> is a C
478 1.2 christos library that reads <abbr>TZif</abbr> files and converts
479 1.2 christos timestamps from one time zone or format to another.
480 1.1 christos It is used by <a href="https://secure.php.net"><abbr
481 1.1 christos title="PHP: Hypertext Preprocessor">PHP</abbr></a>,
482 1.1 christos <a href="https://hhvm.com"><abbr title="HipHop Virtual Machine">HHVM</abbr></a>,
483 1.1 christos and <a href="https://www.mongodb.com">MongoDB</a>.
484 1.1 christos It is freely available under the <abbr>MIT</abbr> license.</li>
485 1.1 christos <li><a href="https://github.com/bigeasy/timezone">Timezone</a> is a
486 1.1 christos JavaScript library that supports date arithmetic that is time zone
487 1.1 christos aware. It is freely available under the <abbr>MIT</abbr> license.</li>
488 1.1 christos <li>Tcl, mentioned <a href="#Tcl">above</a>, also contains a
489 1.2 christos <abbr>TZif</abbr> file reader.</li>
490 1.4 christos <li><a href="https://metacpan.org/pod/DateTime::TimeZone::Tzfile">
491 1.1 christos DateTime::TimeZone::Tzfile</a>
492 1.2 christos is a <abbr>TZif</abbr> file reader written in Perl.
493 1.1 christos It is freely available under the same terms as Perl
494 1.1 christos (dual <abbr>GPL</abbr> and Artistic license).</li>
495 1.1 christos <li>The
496 1.1 christos public-domain <a href="https://github.com/dbaron/tz.js">tz.js</a>
497 1.1 christos library contains a Python tool that
498 1.2 christos converts <abbr>TZif</abbr> data into
499 1.1 christos <abbr>JSON</abbr>-format data suitable for use
500 1.1 christos in its JavaScript library for time zone conversion. Dates before 1970
501 1.1 christos are not supported.</li>
502 1.1 christos <li>The <a
503 1.1 christos href="https://hackage.haskell.org/package/timezone-olson">timezone-olson</a>
504 1.1 christos package contains <a href="https://www.haskell.org">Haskell</a> code that
505 1.2 christos parses and uses <abbr>TZif</abbr> data. It is freely
506 1.1 christos available under a <abbr>BSD</abbr>-style license.</li>
507 1.1 christos </ul>
508 1.1 christos <h2 id="software">Other <code><abbr>tz</abbr></code>-based time zone software</h2>
509 1.1 christos <ul>
510 1.1 christos <li><a href="https://foxclocks.org">FoxClocks</a>
511 1.1 christos is an extension for <a href="https://www.google.com/chrome/">Google
512 1.1 christos Chrome</a> and for <a
513 1.1 christos href="https://developer.mozilla.org/en-US/docs/Mozilla/Tech/Toolkit_API">Mozilla
514 1.1 christos Toolkit</a> applications like <a
515 1.1 christos href="https://www.mozilla.org/en-US/firefox/new/">Firefox</a> and <a
516 1.1 christos href="https://www.mozilla.org/en-US/thunderbird/">Thunderbird</a>.
517 1.1 christos It displays multiple clocks in the application window, and has a mapping
518 1.1 christos interface to <a href="https://www.google.com/earth/">Google Earth</a>.
519 1.1 christos It is freely available under the <abbr>GPL</abbr>.</li>
520 1.1 christos <li><a href="https://golang.org">Go programming language</a>
521 1.1 christos implementations contain a copy of a 32-bit subset of a recent
522 1.1 christos <code><abbr>tz</abbr></code> database in a
523 1.1 christos Go-specific format.</li>
524 1.1 christos <li><a
525 1.1 christos href="http://users.skynet.be/Peter.Verthez/projects/intclock/">International
526 1.1 christos clock (intclock)</a> is a clock that displays multiple time zones on
527 1.1 christos <abbr>GNU</abbr>/Linux and similar systems. It is freely available
528 1.1 christos under the <abbr>GPL</abbr>.</li>
529 1.1 christos <li>Microsoft Windows 8.1
530 1.1 christos and later has <code><abbr>tz</abbr></code> data and <abbr>CLDR</abbr>
531 1.3 christos data (mentioned <a href="#CLDR">below</a>) used by the
532 1.3 christos <a href="https://en.wikipedia.org/wiki/Windows_Runtime">Windows Runtime</a> /
533 1.3 christos <a href="https://en.wikipedia.org/wiki/Universal_Windows_Platform">Universal Windows Platform</a> classes
534 1.3 christos <a href="https://docs.microsoft.com/uwp/api/Windows.Globalization.DateTimeFormatting.DateTimeFormatter"><code>DateTimeFormatter</code></a> and
535 1.3 christos <a href="https://docs.microsoft.com/uwp/api/windows.globalization.calendar"><code>Calendar</code></a>.
536 1.1 christos <a id="System.TimeZoneInfo"
537 1.1 christos href="https://blogs.msdn.microsoft.com/bclteam/2007/06/07/exploring-windows-time-zones-with-system-timezoneinfo-josh-free/">Exploring
538 1.1 christos Windows Time Zones with <code>System.TimeZoneInfo</code></a> describes
539 1.1 christos the older, proprietary method of Microsoft Windows 2000 and later,
540 1.1 christos which stores time zone data in the
541 1.1 christos <a href="https://en.wikipedia.org/wiki/Windows_Registry">Windows Registry</a>. The
542 1.1 christos <a
543 1.1 christos href="https://unicode.org/cldr/charts/latest/supplemental/zone_tzid.html">Zone →
544 1.1 christos Tzid table</a> or <a
545 1.1 christos href="https://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml"><abbr>XML</abbr>
546 1.1 christos file</a> of the <abbr>CLDR</abbr> data maps proprietary zone IDs
547 1.1 christos to <code><abbr>tz</abbr></code> names.
548 1.3 christos These mappings can be performed programmatically via the <a href="https://github.com/mj1856/TimeZoneConverter">TimeZoneConverter</a> .NET library,
549 1.3 christos or the ICU Java and C++ libraries mentioned <a href="#ICU">above</a>.
550 1.1 christos <li><a
551 1.1 christos href="https://www.oracle.com/java/index.html">Oracle
552 1.1 christos Java</a> contains a copy of a subset of a recent
553 1.1 christos <code><abbr>tz</abbr></code> database in a
554 1.1 christos Java-specific format.</li>
555 1.2 christos <li><a href="https://relativedata.com/page/Time-Zone-Master">Time Zone
556 1.1 christos Master</a> is a Microsoft Windows clock program that can automatically
557 1.4 christos download, compile and use <code><abbr>tz</abbr></code> releases.
558 1.4 christos The Basic version is free.</li>
559 1.1 christos <li><a
560 1.1 christos href="http://veladg.com/velaterra.html">VelaTerra</a> is
561 1.1 christos a macOS program. Its developers
562 1.1 christos <a href="http://veladg.com/tzoffer.html">offer free
563 1.1 christos licenses</a> to <code><abbr>tz</abbr></code> contributors.</li>
564 1.1 christos </ul>
565 1.1 christos <h2 id="other-dbs">Other time zone databases</h2>
566 1.1 christos <ul>
567 1.1 christos <li><a href="https://www.astro.com/atlas">Time-zone Atlas</a>
568 1.4 christos is Astrodienst's Web version of Shanks and Pottenger's out-of-print
569 1.4 christos time zone history atlases
570 1.4 christos <a href="https://www.worldcat.org/oclc/468828649">for the US</a> and
571 1.4 christos <a href="https://www.worldcat.org/oclc/76950459">for the world</a>,
572 1.4 christos now published in <a
573 1.1 christos href="https://astrocom.com/astrology-products/software/acs-atlas-software">software</a>
574 1.1 christos form by <a href="https://astrocom.com">ACS-Starcrafts</a>.
575 1.4 christos Although these extensive atlases
576 1.4 christos <a href="https://astrologynewsservice.com/opinion/how-astrologers-contributed-to-the-information-age-a-brief-history-of-time/">were
577 1.4 christos sources for much of the older <code><abbr>tz</abbr></code> data</a>,
578 1.4 christos they are unreliable as Shanks appears to have
579 1.1 christos guessed many <abbr>UT</abbr> offsets and transitions. The atlases cite no
580 1.1 christos sources and do not indicate which entries are guesswork.</li>
581 1.1 christos <li><a href="https://en.wikipedia.org/wiki/HP-UX">HP-UX</a> has a database in
582 1.1 christos its own <code>tztab</code>(4) format.</li>
583 1.1 christos <li>Microsoft Windows has proprietary data mentioned
584 1.1 christos <a href="#System.TimeZoneInfo">above</a>.</li>
585 1.1 christos <li><a href="https://www.worldtimeserver.com">World Time Server</a>
586 1.1 christos is another time zone database.</li>
587 1.1 christos <li>The <a
588 1.1 christos href="https://www.iata.org/publications/store/Pages/standard-schedules-information.aspx">Standard
589 1.1 christos Schedules Information Manual</a> of the
590 1.1 christos International Air Transport Association
591 1.1 christos gives current time zone rules for airports served by commercial aviation.</li>
592 1.1 christos </ul>
593 1.1 christos <h2 id="maps">Maps</h2>
594 1.1 christos <ul>
595 1.1 christos <li>The <a href="https://www.cia.gov/index.html">United States Central
596 1.1 christos Intelligence Agency (<abbr
597 1.1 christos title="Central Intelligence Agency">CIA</abbr>)</a> publishes a <a
598 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
599 1.1 christos zone map</a>; the
600 1.1 christos <a
601 1.1 christos href="https://www.lib.utexas.edu/maps/world.html">Perry–Castañeda
602 1.1 christos Library Map Collection</a>
603 1.1 christos of the University of Texas at Austin has copies of
604 1.1 christos recent editions.
605 1.1 christos The pictorial quality is good,
606 1.1 christos but the maps do not indicate daylight saving time,
607 1.1 christos and parts of the data are a few years out of date.</li>
608 1.1 christos <li><a href="https://www.worldtimezone.com">Current time around the world
609 1.1 christos and standard time zones map of the world</a>
610 1.1 christos has several fancy time zone maps; it covers Russia particularly well.
611 1.1 christos The maps' pictorial quality is not quite as good as the
612 1.1 christos <abbr>CIA</abbr>'s
613 1.1 christos but the maps are more up to date.</li>
614 1.1 christos <li><a
615 1.1 christos href="https://blog.poormansmath.net/how-much-is-time-wrong-around-the-world/">How
616 1.1 christos much is time wrong around the world?</a> maps the difference between
617 1.1 christos mean solar and standard time, highlighting areas such as western China
618 1.1 christos where the two differ greatly. It's a bit out of date, unfortunately.</li>
619 1.1 christos </ul>
620 1.1 christos <h2 id="boundaries">Time zone boundaries</h2>
621 1.2 christos <p>Geographical boundaries between timezones are available
622 1.1 christos from several <a href="https://en.wikipedia.org/wiki/Geolocation">geolocation</a>
623 1.1 christos services and other sources.</p>
624 1.1 christos <ul>
625 1.1 christos <li><a href="https://github.com/evansiroky/timezone-boundary-builder">Timezone
626 1.1 christos Boundary Builder</a> extracts
627 1.1 christos <a href="https://www.openstreetmap.org">Open Street Map</a> data to build
628 1.2 christos boundaries of <code><abbr>tzdb</abbr></code> timezones.
629 1.1 christos Its code is freely available under the <abbr>MIT</abbr> license, and
630 1.1 christos its data entries are freely available under the
631 1.1 christos <a href="https://opendatacommons.org/licenses/odbl/">Open Data Commons
632 1.1 christos Open Database License</a>. The maps' borders appear to be quite accurate.</li>
633 1.1 christos <li>Programmatic interfaces that map geographical coordinates via tz_world to
634 1.2 christos <code><abbr>tzdb</abbr></code> timezones include:
635 1.1 christos <ul>
636 1.1 christos <li><a href="https://github.com/mj1856/GeoTimeZone">GeoTimeZone</a> is
637 1.1 christos written in <a
638 1.1 christos href="https://en.wikipedia.org/wiki/C_Sharp_(programming_language)">C#</a>
639 1.1 christos and is freely available under the <abbr>MIT</abbr> license.</li>
640 1.1 christos <li>The <a href="https://github.com/bradfitz/latlong">latlong package</a>
641 1.1 christos is written in Go and is freely available under the Apache License.</li>
642 1.1 christos <li><a href="https://github.com/drtimcooper/LatLongToTimezone">LatLongToTimezone</a>,
643 1.1 christos in both Java and
644 1.1 christos <a href="https://en.wikipedia.org/wiki/Swift_(programming_language)">Swift</a>
645 1.1 christos form, is freely available under the MIT license.</li>
646 1.1 christos <li>For <a href="https://nodejs.org/en/">Node.js</a>,
647 1.1 christos the <a href="https://www.npmjs.com/package/geo-tz">geo-tz module</a>
648 1.1 christos is freely available under the MIT license, and
649 1.1 christos the <a href="https://www.npmjs.com/package/tz-lookup">tz-lookup module</a>
650 1.1 christos is in the public domain.</li>
651 1.1 christos <li>The <a
652 1.1 christos href="https://github.com/MrMinimal64/timezonefinder">timezonefinder</a>
653 1.1 christos library for Python is freely available under the MIT license.
654 1.1 christos <li>The <a
655 1.1 christos href="https://github.com/gunyarakun/timezone_finder">timezone_finder</a>
656 1.1 christos library for Ruby is freely available under the MIT license.</li>
657 1.1 christos </ul></li>
658 1.1 christos <li>Free access via a network API, if you register a key, is provided by
659 1.4 christos the <a
660 1.4 christos href="https://www.geonames.org/export/web-services.html#timezone">GeoNames
661 1.4 christos Timezone web service</a>, the <a
662 1.4 christos href="https://developers.google.com/maps/documentation/timezone/intro">Google
663 1.4 christos Maps Time Zone API</a>, and
664 1.1 christos the <a href="https://timezonedb.com">Time Zone Database & API</a>.
665 1.1 christos Commercial network API access is provided
666 1.1 christos by <a href="https://askgeo.com">AskGeo</a>
667 1.1 christos and <a href="https://www.geogarage.com/blog/news-1/post/geogarage-time-zone-api-31">GeoGarage</a>.
668 1.1 christos </li>
669 1.1 christos <li>"<a
670 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
671 1.1 christos to get a time zone from a location using latitude and longitude
672 1.1 christos coordinates?</a>" discusses other geolocation possibilities.</li>
673 1.1 christos <li><a href="http://statoids.com/statoids.html">Administrative
674 1.1 christos Divisions of Countries ("Statoids")</a> lists
675 1.1 christos political subdivision data related to time zones.</li>
676 1.1 christos <li><a href="http://home.kpn.nl/vanadovv/time/Multizones.html">Time
677 1.1 christos zone boundaries for multizone countries</a> summarizes legal
678 1.1 christos boundaries between time zones within countries.</li>
679 1.1 christos <li><a href="http://manifold.net/info/freestuff.shtml">Manifold Software
680 1.1 christos – GIS and Database Tools</a> includes a Manifold-format map of
681 1.1 christos world time zone boundaries distributed under the
682 1.1 christos <abbr>GPL</abbr>.</li>
683 1.1 christos <li>A ship within the <a
684 1.1 christos href="https://en.wikipedia.org/wiki/Territorial_waters">territorial
685 1.1 christos waters</a> of any nation uses that nation's time. In international
686 1.1 christos waters, time zone boundaries are meridians 15° apart, except that
687 1.1 christos <abbr>UT</abbr>−12 and <abbr>UT</abbr>+12 are each 7.5°
688 1.1 christos wide and are separated by
689 1.1 christos the 180° meridian (not by the International Date Line, which is
690 1.1 christos for land and territorial waters only). A captain can change ship's
691 1.1 christos clocks any time after entering a new time zone; midnight changes are
692 1.1 christos common.</li>
693 1.1 christos </ul>
694 1.1 christos <h2 id="civil">Civil time concepts and history</h2>
695 1.1 christos <ul>
696 1.1 christos <li><a href="https://www.nist.gov/pml/time-and-frequency-division/popular-links/walk-through-time">A
697 1.1 christos Walk through Time</a>
698 1.1 christos surveys the evolution of timekeeping.</li>
699 1.4 christos <li>The history of daylight saving time is surveyed in <a
700 1.4 christos href="http://www.webexhibits.org/daylightsaving/">About Daylight
701 1.4 christos Saving Time – History, rationale, laws & dates</a> and summarized in
702 1.4 christos <a href="http://seizethedaylight.com/dst/">A Brief
703 1.4 christos History of Daylight Saving Time</a>.</li>
704 1.4 christos <li><a href="https://www.laphamsquarterly.org/roundtable/time-lords">Time
705 1.4 christos Lords</a> discusses how authoritarians manipulate civil time.</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="https://www.staff.science.uu.nl/~gent0113/idl/idl.htm">A History of
710 1.1 christos the International Date Line</a> tells the story of the most important
711 1.1 christos time zone boundary.</li>
712 1.1 christos <li><a href="http://statoids.com/tconcept.html">Basic Time
713 1.1 christos Zone Concepts</a> discusses terminological issues behind time zones.</li>
714 1.1 christos </ul>
715 1.1 christos <h2 id="national">National histories of legal time</h2>
716 1.1 christos <dl>
717 1.1 christos <dt>Australia</dt>
718 1.1 christos <dd>The Parliamentary Library has commissioned a <a
719 1.1 christos href="https://www.aph.gov.au/binaries/library/pubs/rp/2009-10/10rp10.pdf">research
720 1.1 christos paper on daylight saving time in Australia</a>.
721 1.1 christos The Bureau of Meteorology publishes a list of <a
722 1.1 christos href="http://www.bom.gov.au/climate/averages/tables/dst_times.shtml">Implementation
723 1.1 christos Dates of Daylight Savings Time within Australia</a>.</dd>
724 1.1 christos <dt>Belgium</dt>
725 1.1 christos <dd>The Royal Observatory of Belgium maintains a table of <a
726 1.4 christos href="https://www.astro.oma.be/GENERAL/INFO/nli001a.html"
727 1.1 christos hreflang="nl">time in Belgium (in Dutch)</a>.</dd>
728 1.1 christos <dt>Brazil</dt>
729 1.1 christos <dd>The Time Service Department of the National Observatory
730 1.1 christos records <a href="http://pcdsh01.on.br/DecHV.html"
731 1.1 christos hreflang="pt-BR">Brazil's daylight saving time decrees (in
732 1.1 christos Portuguese)</a>.</dd>
733 1.1 christos <dt>Canada</dt>
734 1.1 christos <dd>National Research Council Canada publishes current
735 1.1 christos and some older information about <a
736 1.1 christos href="https://www.nrc-cnrc.gc.ca/eng/services/time/time_zones.html">time
737 1.1 christos zones & daylight saving time</a>.</dd>
738 1.1 christos <dt>Chile</dt>
739 1.1 christos <dd>The Hydrographic and Oceanographic Service of the Chilean Navy publishes a
740 1.4 christos <a href="https://www.horaoficial.cl/historia_hora.html" hreflang="es">history of
741 1.1 christos Chile's official time (in Spanish)</a>.</dd>
742 1.3 christos <dt>China</dt>
743 1.3 christos <dd>The Hong Kong Observatory maintains a
744 1.3 christos <a href="https://www.hko.gov.hk/gts/time/Summertime.htm">history of
745 1.3 christos summer time in Hong Kong</a>,
746 1.3 christos and Macau's Meteorological and Geophysical Bureau maintains a <a
747 1.3 christos href="http://www.smg.gov.mo/smg/geophysics/e_t_Summer%20Time.htm">similar
748 1.3 christos history for Macau</a>.
749 1.3 christos Unfortunately the latter is incomplete and has errors.</dd>
750 1.1 christos <dt>Czech Republic</dt>
751 1.1 christos <dd><a href="https://kalendar.beda.cz/kdy-zacina-a-konci-letni-cas"
752 1.1 christos hreflang="cs">When daylight saving time starts and ends (in Czech)</a>
753 1.1 christos summarizes and cites historical DST regulations.</dd>
754 1.1 christos <dt>Germany</dt>
755 1.1 christos <dd>The National Institute for Science and Technology maintains the <a
756 1.1 christos href="https://www.ptb.de/cms/en/fachabteilungen/abt4/fb-44/ag-441/realisation-of-legal-time-in-germany.html">Realisation
757 1.1 christos of Legal Time in Germany</a>.</dd>
758 1.1 christos <dt>Israel</dt>
759 1.1 christos <dd>The Interior Ministry periodically issues <a
760 1.1 christos href="ftp://ftp.cs.huji.ac.il/pub/tz/announcements"
761 1.1 christos hreflang="he">announcements (in Hebrew)</a>.</dd>
762 1.1 christos <dt>Italy</dt>
763 1.1 christos <dd>The National Institute of Metrological Research maintains a
764 1.4 christos <a href="http://oldsite.inrim.it/res/tf/ora_legale_i.shtml" hreflang="it">table
765 1.4 christos of civil time (in Italian)</a>.</dd>
766 1.2 christos <dt>Malaysia</dt>
767 1.2 christos <dd>See Singapore <a href="#Singapore">below</a>.</dd>
768 1.1 christos <dt>Mexico</dt>
769 1.1 christos <dd>The Investigation and Analysis Service of the Mexican Library of
770 1.1 christos Congress has published a <a
771 1.1 christos href="http://www.diputados.gob.mx/bibliot/publica/inveyana/polisoc/horver/index.htm"
772 1.1 christos hreflang="es">history of Mexican local time (in Spanish)</a>.</dd>
773 1.1 christos <dt>Netherlands</dt>
774 1.1 christos <dd><a href="https://www.staff.science.uu.nl/~gent0113/wettijd/wettijd.htm"
775 1.1 christos hreflang="nl">Legal time in the Netherlands (in Dutch)</a>
776 1.1 christos covers the history of local time in the Netherlands from ancient times.</dd>
777 1.1 christos <dt>New Zealand</dt>
778 1.1 christos <dd>The Department of Internal Affairs maintains a brief <a
779 1.1 christos href="https://www.dia.govt.nz/Daylight-Saving-History">History of
780 1.1 christos Daylight Saving</a>. The privately-maintained <a
781 1.1 christos href="http://astrologyschool.com/nztime.html">History of New Zealand
782 1.1 christos time</a> has more details.</dd>
783 1.1 christos <dt>Singapore</dt>
784 1.1 christos <dd><a id="Singapore"
785 1.1 christos href="http://www.math.nus.edu.sg/aslaksen/teaching/timezone.html">Why
786 1.1 christos is Singapore in the "Wrong" Time Zone?</a> details the
787 1.1 christos history of legal time in Singapore and Malaysia.</dd>
788 1.1 christos <dt>United Kingdom</dt>
789 1.1 christos <dd><a
790 1.1 christos href="https://www.polyomino.org.uk/british-time/">History of
791 1.1 christos legal time in Britain</a> discusses in detail the country
792 1.1 christos with perhaps the best-documented history of clock adjustments.
793 1.1 christos The National Physical Laboratory also maintains an <a
794 1.1 christos href="http://www.npl.co.uk/educate-explore/what-is-time/archive-of-summer-time-dates">Archive
795 1.1 christos of Summer time dates</a>.</dd>
796 1.1 christos <dt>United States</dt>
797 1.1 christos <dd>The Department of Transportation's <a
798 1.1 christos href="https://www.transportation.gov/regulations/recent-time-zone-proceedings">Recent
799 1.1 christos Time Zone Proceedings</a> lists changes to time zone boundaries.</dd>
800 1.1 christos <dt>Uruguay</dt>
801 1.1 christos <dd>The Oceanography, Hydrography, and Meteorology Service of the Uruguayan
802 1.1 christos Navy (SOHMA) publishes an annual <a
803 1.1 christos href="http://www.armada.mil.uy/Pagina/institucion/dimat/sohma/almanaque.html" hreflang="es">almanac
804 1.1 christos (in Spanish)</a>.</dd>
805 1.1 christos </dl>
806 1.1 christos <h2 id="precision">Precision timekeeping</h2>
807 1.1 christos <ul>
808 1.1 christos <li><a
809 1.1 christos href="http://leapsecond.com/hpan/an1289.pdf">The
810 1.1 christos Science of Timekeeping</a> is a thorough introduction
811 1.1 christos to the theory and practice of precision timekeeping.</li>
812 1.1 christos <li><a href="https://doi.org/10.1007/978-3-319-59909-0">The Science of
813 1.1 christos Time 2016</a> contains several freely-readable papers.</li>
814 1.1 christos <li><a href="http://www.ntp.org"><abbr
815 1.1 christos title="Network Time Protocol">NTP</abbr>: The Network
816 1.1 christos Time Protocol</a> (Internet <abbr>RFC</abbr> 5905)
817 1.1 christos discusses how to synchronize clocks of
818 1.1 christos Internet hosts.</li>
819 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>
820 1.2 christos family of software algorithms can achieve accuracy to a few tens of
821 1.2 christos nanoseconds in scalable server farms without special hardware.</li>
822 1.1 christos <li>The <a
823 1.1 christos href="https://www.nist.gov/intelligent-systems-division/ieee-1588">Precision
824 1.1 christos Time Protocol</a> (<abbr
825 1.1 christos title="Institute of Electrical and Electronics Engineers">IEEE</abbr> 1588)
826 1.2 christos can achieve submicrosecond clock accuracy on a local area network
827 1.2 christos with special-purpose hardware.</li>
828 1.1 christos <li><a
829 1.1 christos href="https://tools.ietf.org/html/rfc4833">Timezone
830 1.1 christos Options for <abbr title="Dynamic Host Configuration Protocol">DHCP</abbr></a>
831 1.1 christos (Internet <abbr>RFC</abbr> 4833)
832 1.1 christos specifies a <a
833 1.1 christos href="https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol"><abbr>DHCP</abbr></a>
834 1.1 christos option for a server to configure
835 1.1 christos a client's time zone and daylight saving settings automatically.</li>
836 1.1 christos <li><a
837 1.1 christos href="https://www.cv.nrao.edu/~rfisher/Ephemerides/times.html">Astronomical
838 1.1 christos Times</a> explains more abstruse astronomical time scales like
839 1.1 christos <abbr title="Terrestrial Dynamic Time">TDT</abbr>,
840 1.1 christos <abbr title="Geocentric Coordinate Time">TCG</abbr>, and
841 1.1 christos <abbr title="Barycentric Dynamic Time">TDB</abbr>.
842 1.1 christos <a href="https://www.ucolick.org/~sla/leapsecs/timescales.html">Time
843 1.1 christos Scales</a> goes into more detail, particularly for historical variants.</li>
844 1.1 christos <li>The <a href="https://www.iau.org"><abbr
845 1.1 christos title="International Astronomical Union">IAU</abbr></a>'s <a
846 1.1 christos href="http://www.iausofa.org"><abbr
847 1.1 christos title="Standards Of Fundamental Astronomy">SOFA</abbr></a>
848 1.1 christos collection contains C and <a
849 1.1 christos href="https://en.wikipedia.org/wiki/Fortran">Fortran</a>
850 1.1 christos code for converting among time scales like
851 1.1 christos <abbr title="International Atomic Time">TAI</abbr>,
852 1.1 christos <abbr>TDB</abbr>, <abbr>TDT</abbr> and
853 1.1 christos <abbr>UTC</abbr>.</li>
854 1.1 christos <li><a
855 1.1 christos href="https://www.giss.nasa.gov/tools/mars24/help/notes.html">Mars24 Sunclock
856 1.1 christos – Time on Mars</a> describes Airy Mean Time (<abbr>AMT</abbr>) and the
857 1.1 christos diverse local time
858 1.1 christos scales used by each landed mission on Mars.</li>
859 1.1 christos <li><a href="http://leapsecond.com">LeapSecond.com</a> is
860 1.1 christos dedicated not only to leap seconds but to precise time and frequency
861 1.1 christos in general. It covers the state of the art in amateur timekeeping, and
862 1.1 christos how the art has progressed over the past few decades.</li>
863 1.1 christos <li><a
864 1.1 christos href="https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html"><abbr
865 1.1 christos title="International Earth Rotation and Reference Systems Service">IERS</abbr>
866 1.1 christos Bulletins</a> contains official publications of the International
867 1.1 christos Earth Rotation and Reference Systems Service, which decides when leap
868 1.4 christos seconds occur. The <code><abbr>tz</abbr></code> code and data support leap seconds
869 1.1 christos via an optional "<code>right</code>" configuration, as opposed to the
870 1.1 christos default "<code>posix</code>" configuration.</li>
871 1.1 christos <li><a href="https://developers.google.com/time/smear">Leap Smear</a>
872 1.1 christos discusses how to gradually adjust <abbr>POSIX</abbr> clocks near a
873 1.1 christos leap second so that they disagree with <abbr>UTC</abbr> by at most a
874 1.1 christos half second, even though every <abbr>POSIX</abbr> minute has exactly
875 1.4 christos sixty seconds. This approach works with the default <code><abbr>tz</abbr></code>
876 1.1 christos "<code>posix</code>" configuration, is <a
877 1.1 christos href="http://bk1.ntp.org/ntp-stable/README.leapsmear">supported</a> by
878 1.1 christos the <abbr>NTP</abbr> reference implementation, and is used by major
879 1.1 christos cloud service providers.</li>
880 1.1 christos <li>The <a
881 1.1 christos href="https://pairlist6.pair.net/mailman/listinfo/leapsecs">Leap
882 1.1 christos Second Discussion List</a> covers <a
883 1.1 christos href="https://www2.unb.ca/gge/Resources/gpsworld.november99.pdf">McCarthy
884 1.1 christos and Klepczynski's 1999 proposal to discontinue leap seconds</a>,
885 1.1 christos discussed further in
886 1.1 christos <a href="https://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf">The
887 1.1 christos leap second: its history and possible future</a>.
888 1.1 christos <a href="https://www.ucolick.org/~sla/leapsecs/"><abbr>UTC</abbr>
889 1.1 christos might be redefined
890 1.1 christos without Leap Seconds</a> gives pointers on this
891 1.1 christos contentious issue, which was active until 2015 and could become active
892 1.1 christos again.</li>
893 1.1 christos </ul>
894 1.1 christos <h2 id="notation">Time notation</h2>
895 1.1 christos <ul>
896 1.1 christos <li>The <a id="CLDR" href="http://cldr.unicode.org">Unicode Common Locale Data
897 1.1 christos Repository (<abbr>CLDR</abbr>) Project</a> has localizations for time
898 1.1 christos zone names, abbreviations, identifiers, and formats. For example, it
899 1.1 christos contains French translations for "Eastern European Summer Time",
900 1.1 christos "<abbr title="Eastern European Summer Time">EEST</abbr>", and
901 1.1 christos "Bucharest". Its
902 1.1 christos <a href="https://unicode.org/cldr/charts/latest/by_type/">by-type
903 1.1 christos charts</a> show these values for many locales. Data values are available in
904 1.1 christos both <abbr title="Locale Data Markup Language">LDML</abbr>
905 1.1 christos (an <abbr>XML</abbr> format) and <abbr>JSON</abbr>.
906 1.1 christos <li>
907 1.1 christos <a href="https://www.cl.cam.ac.uk/~mgk25/iso-time.html">A summary of
908 1.1 christos the international standard date and time notation</a> is a good
909 1.1 christos summary of
910 1.1 christos <a
911 1.1 christos href="https://www.iso.org/standard/40874.html"><em><abbr>ISO</abbr>
912 1.1 christos 8601:2004 – Data elements and interchange formats – Information
913 1.1 christos interchange – Representation of dates and times</em></a>.</li>
914 1.1 christos <li>
915 1.1 christos <a href="https://www.w3.org/TR/xmlschema-2/#dateTime"><abbr>XML</abbr>
916 1.1 christos Schema: Datatypes – dateTime</a> specifies a format inspired by
917 1.1 christos <abbr>ISO</abbr> 8601 that is in common use in <abbr>XML</abbr> data.</li>
918 1.1 christos <li><a href="https://tools.ietf.org/html/rfc5322#section-3.3">§3.3 of
919 1.1 christos Internet Message Format</a> (Internet <abbr>RFC</abbr> 5322)
920 1.1 christos specifies the time notation used in email and <a
921 1.1 christos href="https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol"><abbr>HTTP</abbr></a>
922 1.1 christos headers.</li>
923 1.1 christos <li>
924 1.1 christos <a href="https://tools.ietf.org/html/rfc3339">Date and Time
925 1.1 christos on the Internet: Timestamps</a> (Internet <abbr>RFC</abbr> 3339)
926 1.1 christos specifies an <abbr>ISO</abbr> 8601
927 1.1 christos profile for use in new Internet
928 1.1 christos protocols.</li>
929 1.1 christos <li>
930 1.1 christos <a href="https://www.hackcraft.net/web/datetime/">Date & Time
931 1.1 christos Formats on the Web</a> surveys web- and Internet-oriented date and time
932 1.1 christos formats.</li>
933 1.1 christos <li>Alphabetic time zone abbreviations should not be used as unique
934 1.1 christos identifiers for <abbr>UT</abbr> offsets as they are ambiguous in
935 1.1 christos practice. For example, in English-speaking North America
936 1.1 christos "<abbr>CST</abbr>" denotes 6 hours behind <abbr>UT</abbr>,
937 1.1 christos but in China it denotes 8 hours ahead of <abbr>UT</abbr>,
938 1.1 christos and French-speaking North Americans prefer
939 1.1 christos "<abbr title="Heure Normale du Centre">HNC</abbr>" to
940 1.1 christos "<abbr>CST</abbr>". The <code><abbr>tz</abbr></code>
941 1.2 christos database contains English abbreviations for many timestamps;
942 1.1 christos unfortunately some of these abbreviations were merely the database maintainers'
943 1.1 christos inventions, and these have been removed when possible.</li>
944 1.1 christos <li>Numeric time zone abbreviations typically count hours east of
945 1.1 christos <abbr>UT</abbr>, e.g., +09 for Japan and
946 1.1 christos −10 for Hawaii. However, the <abbr>POSIX</abbr>
947 1.1 christos <code><abbr>TZ</abbr></code> environment variable uses the opposite convention.
948 1.1 christos For example, one might use <code><abbr>TZ</abbr>="<abbr
949 1.1 christos title="Japan Standard Time">JST</abbr>-9"</code> and
950 1.1 christos <code><abbr>TZ</abbr>="<abbr title="Hawaii Standard Time">HST</abbr>10"</code>
951 1.1 christos for Japan and Hawaii, respectively. If the
952 1.1 christos <code><abbr>tz</abbr></code> database is available, it is usually better to use
953 1.1 christos settings like <code><abbr>TZ</abbr>="Asia/Tokyo"</code> and
954 1.1 christos <code><abbr>TZ</abbr>="Pacific/Honolulu"</code> instead, as this should avoid
955 1.2 christos confusion, handle old timestamps better, and insulate you better from
956 1.1 christos any future changes to the rules. One should never set
957 1.1 christos <abbr>POSIX</abbr> <code><abbr>TZ</abbr></code> to a value like
958 1.1 christos <code>"GMT-9"</code>, though, since this would incorrectly imply that
959 1.1 christos local time is nine hours ahead of <abbr>UT</abbr> and the time zone
960 1.1 christos is called "<abbr>GMT</abbr>".</li>
961 1.1 christos </ul>
962 1.1 christos <h2 id="see-also">See also</h2>
963 1.1 christos <ul>
964 1.1 christos <li><a href="theory.html">Theory and pragmatics of the tz code and data</a></li>
965 1.1 christos <li><a href="tz-art.html">Time and the Arts</a></li>
966 1.1 christos </ul>
967 1.1 christos <hr>
968 1.1 christos <address>
969 1.1 christos This web page is in the public domain, so clarified as of
970 1.1 christos 2009-05-17 by Arthur David Olson.
971 1.1 christos <br>
972 1.1 christos Please send corrections to this web page to the
973 1.1 christos <a href="mailto:tz (a] iana.org">time zone mailing list</a>.
974 1.1 christos </address>
975 1.1 christos </body>
976 1.1 christos </html>
977