Key:timezone
 timezone
|
 |
| Description |
|---|
Indicate the IANA timezone alias of an object. 
|
| Group: properties |
| Used on these elements |
    |
| Status: in use |
| Tools for this tag |
|
The Internet Assigned Numbers Authority (IANA) maintains the Time Zone Database (tz database), which contains code and data that represent the history of local time for locations. This database uses geographical identifiers with a fixed notation in the form of Continent/Capital — for example, America/New_York, Europe/Amsterdam, and Asia/Pyongyang. These identifiers represent areas for which tz database documents the present and historic time zone rules and offsets. Computers use this database extensively to link devices to the proper time zone. When a computer is configured to use of these identifiers, software will automatically use the proper time zone rules, such as 
the offset from UTC, and whether daylight saving time is observed or not. On OpenStreetMap this tz database identifier is stored in timezone=* for regions it applies to.
The word time zone as used in the name of this key can be confusing due to the fact that these are not actual time zones (i.e., they are neither time offsets, like '1 hour after UTC', nor standard time zones such as 'Eastern Time Zone' or 'Central European Time'). Instead, these identifiers point to a set of rules for computing the past and present time.
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