Key:timezone
 timezone
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Indicate the timezone of the object. 
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| Group: properties |
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| Status: in use |
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A 
time zone is a region on Earth, more or less bounded by lines of longitude, that has a uniform, legally mandated standard time, usually referred to as the local time. By convention, the 24 main time zones on Earth compute their local time as an offset from UTC (see also Greenwich Mean Time), each time zone boundary being ostensibly 15 degrees east or west of the preceding one. The reference point for UTC is the Greenwich Meridian (the Prime Meridian), which has a longitude of 0°. Local time is UTC plus the current time zone offset for the location in question. In theory, the increase proceeds eastward from the eastern boundary of the UTC time zone centered on 0°, increasing by one hour for each 15°, up to the International Date Line (longitude 180°). A corresponding one hour decrease relative to UTC occurs every 15° heading westward from the western boundary of the UTC time zone, up to the International Date Line.
How to map
If an entire country, state, province, or other administrative region observes the same time zone, add a timezone=* key to that region's boundary=administrative relation. Set the value to a time zone name assigned by the tz database. If more than one region observes the same time zone, assign the same timezone=* value to each administrative boundary.
If a region is split so that different subareas observe different time zones, add the timezone=* key to each of the subareas' administrative boundaries instead. A data consumer can then union these boundaries into a coherent time zone boundary.
In some cases, a time zone boundary does not neatly correspond to one or more administrative boundaries, necessitating a boundary=timezone relation. For example, an administrative region may not be completely subdivided by subareas, but one of the subareas may observe a different time zone than the rest of the region. Or a time zone boundary may be independent of other boundaries, following a road, river, railway, or survey line.
See also
- https://github.com/evansiroky/timezone-boundary-builder, a project that combines OSM boundaries with tz database