tz_us, an efele.net/tz map

A shapefile of the TZ timezones of the United States

Last data update: July 5, 2013

Last page update: July 5, 2013

The tz_us shapefile captures the boundaries of the TZ timezones of the United States, as of TZ 2012c.

The geometries are entirely derived from the countyp020p and timeznp020 shapefiles provided by the National Atlas.

All the TZ timezones of United States listed in TZ’s zone.tab are represented, except for America/Shiprock which is included in America/Denver.

Snapshot of the shapefile

This is a snaphsot of the shapefile.

 

Known problems

TZ mentions that America/Kentucky/Louisville contains three counties of Indiana and part of Kentucky, but does not describe precisely that part of Kentucky. In the map, it is made of Jefferson county.

In general, towns on or near the boundary of a zone may practically follow the time of a neighboring zone. We do not attempt to record the boundaries at that level of detail. For example, the boundary between America/Los_Angeles and America/Denver follows the Nevada/Utah border; in practice and by law since 1999, the city of West Wendover, Nevada, is part of America/Denver.

 

Logical description of the zones

Except for the areas described below, the TZ timezone is determined from the legal timezone as follows:

Alaska

Arizona

Hawaii

Idaho

Indiana

Kentucky

Michigan

North Dakota

Oregon

Puerto Rico

Virgin Islands

 

Construction of the shapefile

The zip of the ingredients contains a script to build the map, the modified sources.

The starting point is a couple of map layers from the National Atlas:

Unfortunately, these two maps do not work well together: for example, some common boundaries are not digitized in exactly the same way. So the first step was to conflate them. For the County Boundaries layer, the only change was to add intermediate points where a time zone boundary departs from a county boundary. For the Time Zones layer, the change was to replace the common boundaries by the data from the County Boundaries. The resulting shapefiles are part of the ingredients.

The next step is to perform an overlay of the two maps, to progressively assign a tzid to the geometries (identified by a combination of state, county and “modern” timezone, in accordance with the description above), and to finally dissolve on the tzid attribute. For the exact details of the assignments, see the script in the ingredients.


Terms of use

CC0 To the extent possible under law, Eric Muller has waived all copyright and related or neighboring rights to the efele.net/tz maps (comprising the shapefiles, the web pages describing them and the scripts and data used to build them). This work is published from the United States of America.

Note that this does not affect the rights others may have. I am not qualified to determine whether such rights exist.


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