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| <title>Sources for Time Zone and Daylight Saving Time Data</title> |
| <link rel="schema.DC" href="http://purl.org/DC/elements/1.1/"> |
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| <meta name="DC.Creator" content="Eggert, Paul"> |
| <meta name="DC.Contributor" content="Olson, Arthur David"> |
| <meta name="DC.Date" content="2014-05-27"> |
| <meta name="DC.Description" |
| content="Sources of information about time zones and daylight saving time"> |
| <meta name="DC.Identifier" |
| content="http://www.iana.org/time-zones/repository/tz-link.htm"> |
| <meta name="Keywords" |
| content="database,daylight saving,DST,time zone,timezone,tz,zoneinfo"> |
| </head> |
| <body> |
| <h1>Sources for Time Zone and Daylight Saving Time Data</h1> |
| <h2>The <code><abbr title="time zone">tz</abbr></code> database</h2> |
| <p> |
| The <a href="http://en.wikipedia.org/wiki/Public_domain">public-domain</a> |
| time zone database contains code and data |
| that represent the history of local time |
| for many representative locations around the globe. |
| It is updated periodically to reflect changes made by political bodies |
| to <a href="http://en.wikipedia.org/wiki/Time_zone">time zone</a> |
| boundaries, <a |
| href="http://en.wikipedia.org/wiki/Coordinated_Universal_Time"><abbr |
| title="Coordinated Universal Time">UTC</abbr></a> offsets, and |
| <a href="http://en.wikipedia.org/wiki/Daylight_saving">daylight-saving</a> |
| rules. |
| This database (often called <code>zoneinfo</code> or |
| <code><abbr>tz</abbr></code>) |
| is used by several implementations, |
| including |
| <a href="http://www.gnu.org/software/libc/">the |
| <abbr title="GNU's Not Unix">GNU</abbr> |
| C Library</a> (used in |
| <a href="http://www.linux.org/"><abbr>GNU</abbr>/Linux</a>), |
| <a href="http://www.android.com/">Android</a>, |
| <a href="https://developer.mozilla.org/en-US/docs/Mozilla/Firefox_OS">Firefox |
| <abbr title="Operating System">OS</abbr></a>, |
| <a href="http://www.freebsd.org/">Free<abbr |
| title="Berkeley Software Distribution">BSD</abbr></a>, |
| <a href="http://netbsd.org/">Net<abbr>BSD</abbr></a>, |
| <a href="http://openbsd.org/">Open<abbr>BSD</abbr></a>, |
| <a href="http://cygwin.com/">Cygwin</a>, |
| <a href="http://www.delorie.com/djgpp/"><abbr |
| title="DJ's GNU Programming Platform">DJGPP</abbr></a>, |
| <a href="http://en.wikipedia.org/wiki/Symbian">Symbian</a>, |
| <a href="http://en.wikipedia.org/wiki/WebOS"><abbr |
| title="Web Operating System">webOS</abbr></a>, |
| <a href="http://ibm.com/aix"><abbr |
| title="Advanced Interactive eXecutive">AIX</abbr></a>, |
| <a href="http://en.wikipedia.org/wiki/BlackBerry_10">BlackBerry 10</a>, |
| <a href="http://www.apple.com/ios/"><abbr |
| title="iPhone OS">iOS</abbr></a>, |
| <a href="http://h71000.www7.hp.com/">Open<abbr |
| title="Virtual Memory System">VMS</abbr></a>, |
| <a href="http://oracle.com/database">Oracle Database</a>, |
| <a href="http://www.apple.com/osx/"><abbr title="Operating System Ten">OS |
| X</abbr></a>, and |
| <a href="http://oracle.com/solaris">Solaris</a>.</p> |
| <p> |
| Each location in the database represents a national region where all |
| clocks keeping local time have agreed since 1970. |
| Locations are identified by continent or ocean and then by the name of |
| the location, which is typically the largest city within the region. |
| For example, <code>America/New_York</code> |
| represents most of the <abbr title="United States">US</abbr> eastern time zone; |
| <code>America/Phoenix</code> represents most of Arizona, which |
| uses mountain time without daylight saving time (<abbr |
| title="daylight saving time">DST</abbr>); |
| <code>America/Detroit</code> represents most of Michigan, which uses |
| eastern time but with different <abbr>DST</abbr> rules in 1975; |
| and other entries represent smaller regions like Starke County, |
| Indiana, which switched from central to eastern time in 1991 |
| and switched back in 2006. |
| To use the database on an extended <a |
| href="http://en.wikipedia.org/wiki/POSIX"><abbr |
| title="Portable Operating System Interface">POSIX</abbr></a> |
| implementation set the <code><abbr>TZ</abbr></code> |
| environment variable to the location's full name, |
| e.g., <code><abbr>TZ</abbr>="America/New_York"</code>.</p> |
| <p> |
| In the <code><abbr>tz</abbr></code> database's |
| <a href="ftp://ftp.iana.org/tz/releases/"><abbr |
| title="File Transfer Protocol">FTP</abbr> releases</a> |
| the code is in the file <code>tzcode<var>C</var>.tar.gz</code>, |
| where <code><var>C</var></code> is the code's version; |
| similarly, the data are in <code>tzdata<var>D</var>.tar.gz</code>, |
| where <code><var>D</var></code> is the data's version. |
| Since 1996, each version has been a four-digit year followed by |
| lower-case letter (<samp>a</samp> through <samp>z</samp>, |
| then <samp>za</samp> through <samp>zz</samp>, then <samp>zza</samp> |
| through <samp>zzz</samp>, and so on). |
| Convenience links to |
| the <a href="ftp://ftp.iana.org/tz/tzcode-latest.tar.gz">latest |
| code</a> and |
| <a href="ftp://ftp.iana.org/tz/tzdata-latest.tar.gz">latest data</a> revisions |
| are also available. |
| The following <a |
| href="http://en.wikipedia.org/wiki/Unix_shell">shell</a> commands download |
| these files to a <abbr>GNU</abbr>/Linux or similar host; |
| see the downloaded |
| <code>README</code> file for what to do next.</p> |
| <pre style="margin-left: 2em"><code>mkdir tz |
| cd tz |
| <a href="http://www.gnu.org/software/wget/">wget</a> --retr-symlinks 'ftp://ftp.iana.org/tz/tz*-latest.tar.gz' |
| <a href="http://www.gnu.org/software/gzip/">gzip</a> -dc tzcode-latest.tar.gz | <a href="http://www.gnu.org/software/tar/">tar</a> -xf - |
| gzip -dc tzdata-latest.tar.gz | tar -xf - |
| </code></pre> |
| <p> |
| The code and data files can also be obtained from the |
| <a href="http://www.iana.org/time-zones">Time Zone Database website</a> |
| of the <a href="http://www.iana.org">Internet Assigned Numbers |
| Authority (IANA)</a>. |
| An <a href="https://github.com/eggert/tz">unofficial development |
| repository</a> of the code and data is available |
| in <a href="http://git-scm.com/">Git</a> form |
| from <a href="https://github.com/">GitHub</a>; be careful, as this |
| repository is less well tested and probably contains more errors. |
| <p> |
| The code lets you compile the <code><abbr>tz</abbr></code> source files into |
| machine-readable binary files, one for each location. It also lets |
| you read a <code><abbr>tz</abbr></code> binary file and interpret time stamps for that |
| location.</p> |
| <p> |
| The data are by no means authoritative. If you find errors, please |
| send changes to the <a href="mailto:tz@iana.org">time zone |
| mailing list</a>. You can also <a |
| href="http://news.gmane.org/gmane.comp.time.tz">browse recent |
| messages</a> sent to the mailing list, <a |
| href="https://mm.icann.org/mailman/listinfo/tz">subscribe</a> to it, |
| and browse the <a |
| href="http://mm.icann.org/pipermail/tz/">archive of old |
| messages</a>. For further information about updates, please see |
| <a href="http://tools.ietf.org/html/rfc6557">Procedures for |
| Maintaining the Time Zone Database</a> (Internet <abbr |
| title="Request For Comments">RFC</abbr> 6557).</p> |
| <p> |
| The Web has several other sources for time zone and daylight saving time data. |
| Here are some links that may be of interest. |
| </p> |
| <h2>Commentary on the <code><abbr>tz</abbr></code> database</h2> |
| <ul> |
| <li>The article |
| <a href="http://en.wikipedia.org/wiki/Tz_database">tz database</a> is |
| an encyclopedic summary.</li> |
| <li><a href="http://www.cstdbill.com/tzdb/tz-how-to.html">How to Read the |
| tz Database Source Files</a> explains the <code><abbr>tz</abbr></code> |
| database format.</li> |
| <li><a |
| href="http://blog.jonudell.net/2009/10/23/a-literary-appreciation-of-the-olsonzoneinfotz-database/">A |
| literary appreciation of the Olson/Zoneinfo/tz database</a> comments on the |
| database's style.</li> |
| </ul> |
| <h2>Web sites using recent versions of the <code><abbr>tz</abbr></code> database</h2> |
| <p> |
| These are listed roughly in ascending order of complexity and fanciness. |
| </p> |
| <ul> |
| <li><a href="http://time.is/">Time.is</a> shows locations' |
| time and zones in a simple format.</li> |
| <li><a |
| href="http://twiki.org/cgi-bin/xtra/tzdatepick.html">Date and Time Gateway</a> |
| lets you see the <code><abbr>TZ</abbr></code> values directly.</li> |
| <li><a |
| href="http://convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current |
| Time in 1000 Places</a> uses descriptions of the values.</li> |
| <li><a href="http://www.timezoneconverter.com/cgi-bin/tzc.tzc">Time Zone |
| Converter</a> |
| uses a pulldown menu.</li> |
| <li><a href="http://home.kpn.nl/vanadovv/time/TZworld.html">Complete |
| timezone information for all countries</a> displays tables of DST rules. |
| <li><a href="http://timeanddate.com/worldclock/">The World Clock – |
| Time Zones</a> lets you sort zone names and convert times.</li> |
| <li><a href="http://permatime.com/">Permatime</a> generates and views |
| links that refer to a particular point in time and can be displayed in |
| multiple timezones.</li> |
| <li><a href="http://www.zeitverschiebung.net/en/">Time Difference</a> |
| calculates the current time difference between locations.</li> |
| <li><a href="http://www.wx-now.com/">Weather Now</a> lists the weather too.</li> |
| <li><a href="http://worldtime.io/">worldtime.io</a> |
| also contains data about time zone boundaries; it supports queries via place |
| names and shows location maps.</li> |
| </ul> |
| <h2>Other time zone database formats</h2> |
| <ul> |
| <li>The <a href="http://tools.ietf.org/html/rfc5545"> |
| Internet Calendaring and Scheduling Core Object Specification |
| (iCalendar)</a> (Internet <abbr>RFC</abbr> 5445) |
| covers time zone |
| data; see its VTIMEZONE calendar component. |
| The iCalendar format requires specialized parsers and generators; a |
| variant <a href="http://tools.ietf.org/html/rfc6321">xCal</a> |
| (Internet RFC 6321) uses |
| <a href="http://www.w3.org/XML/"><abbr |
| title="Extensible Markup Language">XML</abbr></a> format, and a draft variant |
| <a href="http://datatracker.ietf.org/doc/draft-ietf-jcardcal-jcal/">jCal</a> |
| uses <a href="http://www.json.org/"><abbr |
| title="JavaScript Object Notation">JSON</abbr></a> format. |
| <a href="http://calconnect.org/">CalConnect, The Calendaring and Scheduling |
| Consortium</a> is promoting further work in this area. <a |
| href="http://calconnect.org/publications/icalendartimezoneproblemsandrecommendationsv1.0.pdf">iCalendar |
| TIMEZONE Problems and Recommendations</a> offers guidelines and |
| recommendations for the use of VTIMEZONE and <code><abbr>tz</abbr></code>.</li> |
| <li>CalConnect's <a href="http://calconnect.org/tc-timezone.shtml">TIMEZONE |
| Technical Committee</a> has developed |
| a <a href="http://tools.ietf.org/html/draft-douglass-timezone-service-08">draft |
| timezone service protocol</a>. The committee's earlier <a |
| href="http://calconnect.org/publications/timezoneregistryandservicerecommendationsv1.0.pdf">Timezone |
| Registry and Service Recommendations</a> discusses a |
| strategy for defining and deploying a time zone |
| registration process that would establish unique names for each |
| version of each <code><abbr>tz</abbr></code> zone, along with a polygonal |
| representation of the geographical area corresponding to the |
| zone.</li> |
| <li>The <a |
| href="http://lists.w3.org/Archives/Public/www-rdf-calendar/">www-rdf-calendar</a> |
| list discusses <a |
| href="http://www.w3.org/RDF/"><abbr |
| title="Resource Description Framework">RDF</abbr></a>-based calendar |
| and group scheduling systems, and has a <a |
| href="http://www.w3.org/2002/12/cal/#tzd">workspace on time zone |
| data</a> converted from <code><abbr>tz</abbr></code>. An earlier <a |
| href="http://www.w3.org/2000/01/foo">schema</a> was sketched out.</li> |
| </ul> |
| <h2>Other <code><abbr>tz</abbr></code> compilers</h2> |
| <ul> |
| <li><a href="http://sourceforge.net/projects/vzic/">Vzic iCalendar |
| Timezone Converter</a> describes a <a |
| href="http://en.wikipedia.org/wiki/C_%28programming_language%29">C</a> |
| program that compiles |
| <code><abbr>tz</abbr></code> source into iCalendar-compatible VTIMEZONE files. |
| Vzic is freely |
| available under the <a |
| href="http://www.gnu.org/copyleft/gpl.html"><abbr>GNU</abbr> |
| General Public License (<abbr |
| title="General Public License">GPL</abbr>)</a>.</li> |
| <li><a href="http://sourceforge.net/projects/tzical">tziCal – tz |
| database conversion utility</a> is like Vzic, except for the <a |
| href="http://msdn.microsoft.com/netframework">.NET framework</a>.</li> |
| <li><a |
| href="http://search.cpan.org/dist/DateTime-TimeZone/">DateTime::TimeZone</a> |
| contains a script <code>parse_olson</code> that compiles |
| <code><abbr>tz</abbr></code> source into <a href="http://www.perl.org/">Perl</a> |
| modules. It is part of the Perl <a |
| href="http://datetime.perl.org/">DateTime Project</a>, which is freely |
| available under both the <abbr>GPL</abbr> and the Perl Artistic |
| License. DateTime::TimeZone also contains a script |
| <code>tests_from_zdump</code> that generates test cases for each clock |
| transition in the <code><abbr>tz</abbr></code> database.</li> |
| <li><a href="http://icu-project.org/">International Components for |
| Unicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a |
| href="http://en.wikipedia.org/wiki/Java_%28programming_language%29">Java</a> |
| libraries for internationalization that |
| has a compiler from <code><abbr>tz</abbr></code> source |
| and from <abbr title="Common Locale Data Repository">CLDR</abbr> data |
| (mentioned below) |
| into an <abbr>ICU</abbr>-specific format. |
| <abbr>ICU</abbr> is freely available under a |
| <abbr>BSD</abbr>-style license.</li> |
| <li><a href="http://www.joda.org/joda-time/">Joda Time – Java date |
| and time <abbr title="Application Program Interface">API</abbr></a> |
| contains a class |
| <code>org.joda.time.tz.ZoneInfoCompiler</code> that compiles |
| <code><abbr>tz</abbr></code> source into a Joda-specific binary format. Joda Time |
| is freely available under a <abbr>BSD</abbr>-style license.</li> |
| <li><a href="http://nodatime.org/">Noda Time – Date and time API for |
| .NET</a> and <a href="http://www.babiej.demon.nl/Tz4Net/main.htm">TZ4Net</a> |
| are similar to Joda Time, but for the .NET framework instead of |
| Java. They are freely available under the |
| <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License</a> |
| and a <abbr>BSD</abbr>-style license, respectively.</li> |
| <li><a href="https://github.com/mde/timezone-js">TimezoneJS.Date</a> |
| is a <a href="http://en.wikipedia.org/wiki/JavaScript">JavaScript</a> |
| library that parses <code><abbr>tz</abbr></code> source files and interprets time |
| stamps using an API that is upward compatible with standard JavaScript |
| Dates. It is freely available under the Apache License.</li> |
| <li><a href="http://pytz.sourceforge.net">pytz – World Timezone |
| Definitions for Python</a> compiles <code><abbr>tz</abbr></code> source into |
| <a href="http://python.org/">Python</a>. |
| It is freely available under a <abbr>BSD</abbr>-style license.</li> |
| <li><a href="http://tzinfo.rubyforge.org/">TZInfo – |
| Ruby Timezone Library</a> |
| compiles <code><abbr>tz</abbr></code> source into |
| <a href="http://www.ruby-lang.org/en/">Ruby</a>. |
| It is freely available under the <abbr |
| title="Massachusetts Institute of Technology">MIT</abbr> license.</li> |
| <li>The <a href="http://www.squeaksource.com/Chronos/">Chronos Date/Time |
| Library</a> is |
| a <a href="http://en.wikipedia.org/wiki/Smalltalk">Smalltalk</a> class |
| library that compiles <code><abbr>tz</abbr></code> source into a time |
| zone repository whose format |
| is either proprietary or an <abbr>XML</abbr>-encoded |
| representation.</li> |
| <li>Starting with version 8.5, <a href="http://tcl.tk/">Tcl</a> |
| contains a developer-oriented parser that compiles <code><abbr>tz</abbr></code> |
| source into text files, along with a runtime that can read those |
| files. Tcl is freely available under a <abbr>BSD</abbr>-style |
| license.</li> |
| </ul> |
| <h2>Other <code><abbr>tz</abbr></code> binary file readers</h2> |
| <ul> |
| <li>The <a |
| href="http://www.gnu.org/software/libc/"><abbr>GNU</abbr> C |
| Library</a> |
| has an independent, thread-safe implementation of |
| a <code><abbr>tz</abbr></code> binary file reader. |
| This library is freely available under the |
| <a href="http://www.gnu.org/copyleft/lesser.html"> |
| <abbr>GNU</abbr> Lesser General Public License |
| (<abbr title="Lesser General Public License">LGPL</abbr>)</a>, |
| and is widely used in <abbr>GNU</abbr>/Linux systems.</li> |
| <li><a href="http://www.gnome.org/">GNOME</a>'s Glib has |
| a <code><abbr>tz</abbr></code> binary file reader written in C that |
| creates a <code>GTimeZone</code> object representing sets of UTC offsets. |
| It is freely available under the <abbr>LGPL</abbr>.</li> |
| <li><a href="http://bmsi.com/java/#TZ">ZoneInfo.java</a> |
| is a <code><abbr>tz</abbr></code> binary file reader written in Java. |
| It is freely available under the <abbr>LGPL</abbr>.</li> |
| <li>Tcl, mentioned above, also contains a |
| <code><abbr>tz</abbr></code> binary file reader.</li> |
| <li><a href="http://search.cpan.org/perldoc?DateTime::TimeZone::Tzfile"> |
| DateTime::TimeZone::Tzfile</a> |
| is a <code><abbr>tz</abbr></code> binary file reader written in Perl. |
| It is freely available under the same terms as Perl |
| (dual <abbr>GPL</abbr> and Artistic license).</li> |
| <li>The |
| public-domain <a href="https://github.com/dbaron/tz.js">tz.js</a> |
| library contains a Python tool that |
| converts <code><abbr>tz</abbr></code> binary data into |
| <abbr>JSON</abbr>-format data suitable for use |
| in its JavaScript library for time zone conversion. Dates before 1970 |
| are not supported.</li> |
| <li>The <a |
| href="http://hackage.haskell.org/package/timezone-olson">timezone-olson</a> |
| package contains <a href="http://haskell.org">Haskell</a> code that |
| parses and uses <code><abbr>tz</abbr></code> binary data.</li> |
| </ul> |
| <h2>Other <code><abbr>tz</abbr></code>-based time zone software</h2> |
| <ul> |
| <li><a href="http://foxclocks.org/">FoxClocks</a> |
| is an extension for <a href="http://google.com/chrome">Google |
| Chrome</a> and for <a |
| href="http://developer.mozilla.org/en/docs/Toolkit_API">Mozilla |
| Toolkit</a> applications like <a |
| href="http://mozilla.com/firefox">Firefox</a> and <a |
| href="http://mozilla.com/thunderbird">Thunderbird</a>. |
| It displays multiple clocks in the application window, and has a mapping |
| interface to <a href="http://earth.google.com/">Google Earth</a>. |
| It is freely available under the <abbr>GPL</abbr>.</li> |
| <li><a |
| href="http://users.skynet.be/Peter.Verthez/projects/intclock/">International |
| clock (intclock)</a> is a multi-timezone clock for |
| <abbr>GNU</abbr>/Linux and similar systems. It is freely available |
| under the <abbr>GPL</abbr>.</li> |
| <li><a |
| href="http://www.oracle.com/us/technologies/java/overview/index.html">Oracle |
| Java</a> releases since 1.4 |
| contain a copy of a subset of a recent <code><abbr>tz</abbr></code> database in a |
| Java-specific format.</li> |
| <li><a href="http://kimmo.suominen.com/sw/timezone/">Time Zone</a> is |
| a <a href="http://wordpress.org/">WordPress</a> plugin. It is freely |
| available under a <abbr>BSD</abbr>-style license.</li> |
| <li><a href="http://www.relativedata.com/time-zone-master">Time Zone |
| Master</a> is a Microsoft Windows clock program that can automatically |
| download, compile and use the <code>tzdata<var>D</var>.tar.gz</code> |
| files as they are released. The Basic version is free.</li> |
| <li><a |
| href="http://veladg.com/velaterra.html">VelaTerra</a> is |
| a Mac <abbr>OS X</abbr> program. Its developers |
| <a href="http://veladg.com/tzoffer.html">offer free |
| licenses</a> to <code><abbr>tz</abbr></code> contributors.</li> |
| <li><a |
| href="http://worldtimeexplorer.com/">World Time Explorer</a> is a |
| Microsoft Windows program.</li> |
| </ul> |
| <h2>Other time zone databases</h2> |
| <ul> |
| <li><a href="http://www.astro.com/cgi/aq.cgi">Atlas Query</a> |
| is Astrodienst's Web version of Shanks and Pottenger's |
| time zone history atlases published in both <a |
| href="http://astrocom.com/astrology-products/software/acs-atlas-software">computer</a> |
| and book form (<a |
| href="http://www.astrocom.com/astrology/books/american-atlas">one volume |
| for the U.S.</a>, and <a |
| href="http://www.astrocom.com/astrology/books/international-atlas">one for |
| other locations</a>) by <a |
| href="http://astrocom.com/">Astro Computing Services</a>.</li> |
| <li><a href="http://worldtime.com/">WORLDTIME: interactive atlas, |
| time info, public holidays</a> |
| contains information on local time, sunrise and sunset, |
| and public holidays in several hundred cities around the world.</li> |
| <li><a href="http://worldtimeserver.com/">World Time Server</a> |
| is another time zone database.</li> |
| <li><a href="http://tycho.usno.navy.mil/tzones.html">World Time Zones</a> |
| contains data from the Time Service Department of the |
| <abbr>US</abbr> Naval Observatory, used as the source |
| for the <code><abbr>usno</abbr>*</code> files in |
| the <code><abbr>tz</abbr></code> distribution.</li> |
| <li>The <a href="http://www.iata.org/publications/Pages/ssim.aspx">Standard |
| Schedules Information Manual</a> of the |
| <a href="http://iata.org/index.htm">International Air Transport |
| Association</a> |
| gives current time zone rules for airports served by commercial aviation.</li> |
| <li>Some Microsoft Windows versions contain time zone information in |
| an undocumented format, with <abbr>ID</abbr>s that can be mapped to |
| <code><abbr>TZ</abbr></code> values using the <a |
| href="http://unicode.org/cldr/charts/supplemental/zone_tzid.html">Zone |
| → Tzid table</a> in the <abbr>CLDR</abbr> data mentioned |
| below, or via <a href="http://msdn.microsoft.com/en-us/windows/apps">Windows |
| Store apps</a> classes such as <a |
| href="http://msdn.microsoft.com/en-us/library/windows/apps/dn264145.aspx">DateTimeFormatter</a>.</li> |
| </ul> |
| <h2>Maps</h2> |
| <ul> |
| <li>The <a href="https://www.cia.gov/">United States Central |
| Intelligence Agency (<abbr |
| title="Central Intelligence Agency">CIA</abbr>)</a> publishes a <a |
| href="https://www.cia.gov/library/publications/the-world-factbook/graphics/ref_maps/physical/pdf/standard_time_zones_of_the_world.pdf">time |
| zone map</a>; the |
| <a |
| href="http://www.lib.utexas.edu/maps/world.html">Perry-Castañeda |
| Library Map Collection</a> |
| of the University of Texas at Austin has copies of |
| recent editions. |
| The pictorial quality is good, |
| but the maps do not indicate summer time, |
| and parts of the data are a few years out of date.</li> |
| <li><a href="http://worldtimezone.com/">Current time around the world |
| and standard time zones map of the world</a> |
| has several fancy time zone maps; it covers Russia particularly well. |
| The maps' pictorial quality is not quite as good as the |
| <abbr>CIA</abbr>'s |
| but the maps are more up to date.</li> |
| <li><a href="http://poisson.phc.unipi.it/~maggiolo/index.php/2014/01/how-much-is-time-wrong-around-the-world/">How |
| much is time wrong around the world?</a> maps the difference between |
| mean solar and standard time, highlighting areas such as western China |
| where the two differ greatly.</li> |
| </ul> |
| <h2>Time zone boundaries</h2> |
| <ul> |
| <li><a href="http://efele.net/maps/tz/"><abbr>TZ</abbr> timezones |
| maps</a> contains <a |
| href="http://en.wikipedia.org/wiki/Shapefile">shapefiles</a> of |
| sets of <code><abbr>tz</abbr></code> regions.</li> |
| <li><a href="http://derickrethans.nl/what-time-is-it.html">What Time |
| is It Here?</a> applies <a href="http://www.mongodb.org/">MongoDB</a> |
| geospatial query operators to shapefiles' data.</li> |
| <li><a href="http://statoids.com/statoids.html">Administrative |
| Divisions of Countries ("Statoids")</a> contains lists of |
| political subdivision data related to time zones.</li> |
| <li><a href="http://home.kpn.nl/vanadovv/time/Multizones.html">Time |
| zone boundaries for multizone countries</a> summarizes legal |
| boundaries between time zones within countries.</li> |
| <li>Manifold.net's <a |
| href="http://manifold.net/info/freestuff.shtml">Free Stuff for |
| Manifold System Users</a> includes a Manifold-format map of |
| world time zone boundaries distributed under the |
| <abbr>GPL</abbr>.</li> |
| <li>The <abbr>US</abbr> Geological Survey's National Atlas of |
| the United States |
| publishes the <a href="http://nationalatlas.gov/mld/timeznp.html">Time |
| Zones of the United States</a> in the public domain.</li> |
| <li>The GeoCommunity lists several commercial sources for <a |
| href="http://spatialnews.geocomm.com/features/timezones/">International |
| Time Zones and Time Zone Data</a>.</li> |
| <li>A ship within the <a |
| href="http://en.wikipedia.org/wiki/Territorial_waters">territorial |
| waters</a> of any nation uses that nation's time. In international |
| waters, time zone boundaries are meridians 15° apart, except that |
| <abbr>UTC</abbr>−12 and <abbr>UTC</abbr>+12 are each 7.5° |
| wide and are separated by |
| the 180° meridian (not by the International Date Line, which is |
| for land and territorial waters only). A captain can change ship's |
| clocks any time after entering a new time zone; midnight changes are |
| common.</li> |
| </ul> |
| <h2>Civil time concepts and history</h2> |
| <ul> |
| <li><a href="http://physics.nist.gov/GenInt/Time/time.html">A |
| Walk through Time</a> |
| surveys the evolution of timekeeping.</li> |
| <li><a href="http://webexhibits.org/daylightsaving/">About Daylight |
| Saving Time – History, rationale, laws & dates</a> |
| is an overall history of <abbr>DST</abbr>.</li> |
| <li><a href="http://www.w3.org/TR/timezone/">Working with Time Zones</a> |
| contains guidelines and best practices for software applications that |
| deal with civil time.</li> |
| <li><a href="http://energy.ca.gov/daylightsaving.html">Saving Time, |
| Saving Energy</a> discusses a primary justification for <abbr>DST</abbr>.</li> |
| <li><a href="http://seizethedaylight.com/dst/">A Brief |
| History of Daylight Saving Time</a> summarizes some of the contentious |
| history of <abbr>DST</abbr>.</li> |
| <li><a href="http://toi.inrim.it/uk/toi.html">The |
| Time of Internet</a> |
| describes time zones and daylight saving time, |
| with diagrams. |
| The time zone map is out of date, however.</li> |
| <li><a href="http://www.staff.science.uu.nl/~gent0113/idl/idl.htm">A History of |
| the International Date Line</a> tells the story of the most important |
| time zone boundary.</li> |
| <li><a href="http://statoids.com/tconcept.html">Basic Time |
| Zone Concepts</a> discusses terminological issues behind time zones.</li> |
| </ul> |
| <h2>National histories of legal time</h2> |
| <dl> |
| <dt>Australia</dt> |
| <dd>The Parliamentary Library has commissioned <a |
| href="http://www.aph.gov.au/binaries/library/pubs/rn/2006-07/07rn13.pdf">research |
| note on daylight saving time in Australia</a>. |
| The Bureau of Meteorology publishes a list of <a |
| href="http://www.bom.gov.au/climate/averages/tables/dst_times.shtml">Implementation |
| Dates of Daylight Savings Time within Australia</a>.</dd> |
| <dt>Belgium</dt> |
| <dd>The Royal Observatory of Belgium maintains a table of <a |
| href="http://www.astro.oma.be/GENERAL/INFO/nli001a.html" |
| hreflang="nl">time in Belgium (in Dutch)</a>.</dd> |
| <dt>Brazil</dt> |
| <dd>The Time Service Department of the National Observatory |
| records <a href="http://pcdsh01.on.br/DecHV.html" |
| hreflang="pt-BR">Brazil's daylight saving time decrees (in |
| Portuguese)</a>.</dd> |
| <dt>Canada</dt> |
| <dd>National Research Council Canada publishes current |
| and some older information about <a |
| href="http://www.nrc-cnrc.gc.ca/eng/services/time/time_zones.html">time |
| zones & daylight saving time</a>.</dd> |
| <dt>Chile</dt> |
| <dd>The Chilean Hydrographic and Oceanographic Service publishes a <a |
| href="http://www.horaoficial.cl/historia_hora.html" hreflang="es">history of |
| Chile's official time (in Spanish)</a>.</dd> |
| <dt>Germany</dt> |
| <dd>The National Institute for Science and Technology maintains the <a |
| href="http://www.ptb.de/cms/en/fachabteilungen/abt4/fb-44/ag-441/realisation-of-legal-time-in-germany.html">Realisation |
| of Legal Time in Germany</a>.</dd> |
| <dt>Israel</dt> |
| <dd>The Interior Ministry periodically issues <a |
| href="ftp://ftp.cs.huji.ac.il/pub/tz/announcements" |
| hreflang="he">announcements (in Hebrew)</a>.</dd> |
| <dt>Mexico</dt> |
| <dd>The Investigation and Analysis Service of the Mexican Library of |
| Congress has published a <a |
| href="http://www.diputados.gob.mx/bibliot/publica/inveyana/polisoc/horver/" |
| hreflang="es">history of Mexican local time (in Spanish)</a>.</dd> |
| <dt>Malaysia</dt> |
| <dd>See Singapore below.</dd> |
| <dt>Netherlands</dt> |
| <dd><a href="http://www.staff.science.uu.nl/~gent0113/wettijd/wettijd.htm" |
| hreflang="nl">Legal time in the Netherlands (in Dutch)</a> |
| covers the history of local time in the Netherlands from ancient times.</dd> |
| <dt>New Zealand</dt> |
| <dd>The Department of Internal Affairs maintains a brief <a |
| href="http://www.dia.govt.nz/Daylight-Saving-History">History of |
| Daylight Saving</a>. The privately-maintained <a |
| href="http://astrologyschool.com/nztime.html">History of New Zealand |
| time</a> has more details.</dd> |
| <dt>Singapore</dt> |
| <dd><a |
| href="http://www.math.nus.edu.sg/aslaksen/teaching/timezone.html">Why |
| is Singapore in the "Wrong" Time Zone?</a> details the |
| history of legal time in Singapore and Malaysia.</dd> |
| <dt>United Kingdom</dt> |
| <dd><a |
| href="http://www.polyomino.org.uk/british-time/">History of |
| legal time in Britain</a> discusses in detail the country |
| with perhaps the best-documented history of clock adjustments. |
| The National Physical Laboratory also maintains an <a |
| href="http://www.npl.co.uk/educate-explore/what-is-time/archive-of-summer-time-dates-1916-2006">Archive |
| of Summer time dates</a>.</dd> |
| </dl> |
| <h2>Precision timekeeping</h2> |
| <ul> |
| <li><a |
| href="http://literature.agilent.com/litweb/pdf/5965-7984E.pdf">The |
| Science of Timekeeping</a> is a thorough introduction |
| to the theory and practice of precision timekeeping.</li> |
| <li><a href="http://www.ntp.org/"><abbr |
| title="Network Time Protocol">NTP</abbr>: The Network |
| Time Protocol</a> |
| discusses how to synchronize clocks of |
| Internet hosts.</li> |
| <li><a |
| href="http://tools.ietf.org/html/rfc4833">Timezone |
| Options for <abbr title="Dynamic Host Configuration Protocol">DHCP</abbr></a> |
| (Internet <abbr>RFC</abbr> 4833) |
| specifies a <a |
| href="http://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol"><abbr>DHCP</abbr></a> |
| option for a server to configure |
| a client's time zone and daylight saving settings automatically.</li> |
| <li><a href="http://gauss.gge.unb.ca/GMT.UT.and.the.RGO.html">A Few |
| Facts Concerning <abbr title="Greenwich Mean Time">GMT</abbr>, <abbr |
| title="Universal Time">UT</abbr>, and |
| the <abbr title="Royal Greenwich Observatory">RGO</abbr></a> |
| answers questions like "What is the |
| difference between <abbr>GMT</abbr> and <abbr>UTC</abbr>?"</li> |
| <li><a |
| href="http://www.cv.nrao.edu/~rfisher/Ephemerides/times.html">Astronomical |
| Times</a> explains more abstruse astronomical time scales like |
| <abbr title="Terrestrial Dynamic Time">TDT</abbr>, |
| <abbr title="Geocentric Coordinate Time">TCG</abbr>, and |
| <abbr title="Barycentric Dynamic Time">TDB</abbr>. |
| <a href="http://www.ucolick.org/~sla/leapsecs/timescales.html">Time |
| Scales</a> goes into more detail, particularly for historical variants.</li> |
| <li>The <a href="http://iau.org/"><abbr |
| title="International Astronomical Union">IAU</abbr></a>'s <a |
| href="http://www.iausofa.org/"><abbr |
| title="Standards Of Fundamental Astronomy">SOFA</abbr></a> |
| initiative publishes C and Fortran |
| code for converting among time scales like |
| <abbr title="International Atomic Time">TAI</abbr>, |
| <abbr>TDB</abbr>, <abbr>TDT</abbr> and |
| <abbr>UTC</abbr>.</li> |
| <li><a href="http://www2.jpl.nasa.gov/basics/bsf2-3.php">Basics of |
| Space Flight – Reference Systems – Time Conventions</a> |
| briefly explains interplanetary space flight timekeeping.</li> |
| <li><a |
| href="http://www.giss.nasa.gov/tools/mars24/help/notes.html">Technical |
| Notes on Mars Solar Time as Adopted by the Mars24 Sunclock</a> briefly |
| describes Mars Coordinated Time (<abbr |
| title="Mars Coordinated Time">MTC</abbr>) and the |
| diverse local time |
| scales used by each landed mission on Mars.</li> |
| <li><a href="http://leapsecond.com/">LeapSecond.com</a> is |
| dedicated not only to leap seconds but to precise time and frequency |
| in general. It covers the state of the art in amateur timekeeping, and |
| how the art has progressed over the past few decades.</li> |
| <li><a |
| href="http://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html"><abbr |
| title="International Earth Rotation and Reference Systems Service">IERS</abbr> |
| Bulletins</a> contains official publications of the International |
| Earth Rotation and Reference Systems Service, which decides |
| when leap seconds occur.</li> |
| <li>The <a |
| href="http://six.pairlist.net/mailman/listinfo/leapsecs">Leap |
| Second Discussion List</a> covers <a |
| href="http://gauss.gge.unb.ca/papers.pdf/gpsworld.november99.pdf">McCarthy |
| and Klepczynski's proposal to discontinue leap seconds</a>, |
| discussed further in |
| <a href="http://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf">The |
| leap second: its history and possible future</a>. |
| <a href="http://www.ucolick.org/~sla/leapsecs/"><abbr>UTC</abbr> |
| might be redefined |
| without Leap Seconds</a> gives pointers on this |
| contentious issue.</li> |
| </ul> |
| <h2>Time notation</h2> |
| <ul> |
| <li>The <a href="http://unicode.org/cldr/">Unicode Common Locale Data |
| Repository (<abbr>CLDR</abbr>) Project</a> has localizations for time |
| zone names, abbreviations, identifiers, and formats. For example, it |
| contains French translations for "Eastern European Summer Time", |
| "<abbr title="Eastern European Summer Time">EEST</abbr>", and |
| "Bucharest". Its |
| <a href="http://unicode.org/cldr/charts/by_type/index.html">by-type |
| charts</a> show these values for many locales. Data are available in |
| both <abbr title="Locale Data Markup Language">LDML</abbr> |
| (an <abbr>XML</abbr> format) and <abbr>JSON</abbr>. |
| <li> |
| <a href="http://www.cl.cam.ac.uk/~mgk25/iso-time.html">A summary of |
| the international standard date and time notation</a> is a good |
| summary of |
| <a |
| href="http://www.iso.org/iso/catalogue_detail?csnumber=40874"><abbr |
| title="International Organization for Standardization">ISO</abbr> |
| 8601:2004 – Data elements and interchange formats – Information |
| interchange – Representation of dates and times</a>.</li> |
| <li> |
| <a href="http://www.w3.org/TR/xmlschema-2/#dateTime"><abbr>XML</abbr> |
| Schema: Datatypes – dateTime</a> specifies a format inspired by |
| <abbr>ISO</abbr> 8601 that is in common use in <abbr>XML</abbr> data.</li> |
| <li> |
| <a href="http://tools.ietf.org/html/rfc5322">Internet |
| Message Format</a> (Internet <abbr>RFC</abbr> 5322) §3.3 |
| specifies the time notation used in email and <a |
| href="http://tools.ietf.org/html/rfc2616"><abbr>HTTP</abbr></a> |
| headers.</li> |
| <li> |
| <a href="http://tools.ietf.org/html/rfc3339">Date and Time |
| on the Internet: Timestamps</a> (Internet <abbr>RFC</abbr> 3339) |
| specifies an <abbr>ISO</abbr> 8601 |
| profile for use in new Internet |
| protocols.</li> |
| <li> |
| <a href="http://www.hackcraft.net/web/datetime/">Date & Time |
| Formats on the Web</a> surveys web- and Internet-oriented date and time |
| formats.</li> |
| <li> |
| <a href="http://exit109.com/~ghealton/y2k/yrexamples.html">The |
| Best of Dates, the Worst of Dates</a> covers many problems encountered |
| by software developers when handling dates and time stamps.</li> |
| <li>Alphabetic time zone abbreviations should not be used as unique |
| identifiers for <abbr>UTC</abbr> offsets as they are ambiguous in |
| practice. For example, "<abbr>EST</abbr>" denotes 5 hours behind |
| <abbr>UTC</abbr> in English-speaking North America, but it denotes 10 |
| or 11 hours ahead of <abbr>UTC</abbr> in Australia; and |
| French-speaking North Americans prefer |
| "<abbr title="Heure Normale de l'Est">HNE</abbr>" to |
| "<abbr>EST</abbr>". For <abbr>POSIX</abbr> the <code><abbr>tz</abbr></code> |
| database contains English abbreviations for all time stamps but in |
| many cases these are merely inventions of the database |
| maintainers.</li> |
| <li>Numeric time zone abbreviations typically count hours east of |
| <abbr>UTC</abbr>, e.g., <code>+09</code> for Japan and |
| <code>-10</code> for Hawaii. However, the <abbr>POSIX</abbr> |
| <code><abbr>TZ</abbr></code> environment variable uses the opposite convention. |
| For example, one might use <code><abbr>TZ</abbr>="<abbr |
| title="Japan Standard Time">JST</abbr>-9"</code> and |
| <code><abbr>TZ</abbr>="<abbr title="Hawaii Standard Time">HST</abbr>10"</code> |
| for Japan and Hawaii, respectively. If the |
| <code><abbr>tz</abbr></code> database is available, it is usually better to use |
| settings like <code><abbr>TZ</abbr>="Asia/Tokyo"</code> and |
| <code><abbr>TZ</abbr>="Pacific/Honolulu"</code> instead, as this should avoid |
| confusion, handle old time stamps better, and insulate you better from |
| any future changes to the rules. One should never set |
| <abbr>POSIX</abbr> <code><abbr>TZ</abbr></code> to a value like |
| <code>"GMT-9"</code>, though, since this would falsely claim that |
| local time is nine hours ahead of <abbr>UTC</abbr> and the time zone |
| is called "<abbr>GMT</abbr>".</li> |
| </ul> |
| <h2>Related indexes</h2> |
| <ul> |
| <li><a href="tz-art.htm">Time and the Arts</a></li> |
| <li><a href="http://www.dmoz.org/Reference/Time/">Open Directory – |
| Reference: Time</a></li> |
| <li><a href="http://dir.yahoo.com/Science/Measurements_and_Units/Time">Yahoo! |
| Directory > Science > Measurements and Units > Time</a></li> |
| </ul> |
| <hr> |
| <address> |
| This web page is in the public domain, so clarified as of |
| 2009-05-17 by Arthur David Olson. |
| <br> |
| Please send corrections to this web page to the |
| <a href="mailto:tz@iana.org">time zone mailing list</a>. |
| </address> |
| </body> |
| </html> |