lat/lon to time offset database

[Guy Harris]

On Feb 3, 2011, at 12:22 PM, Alois Treindl wrote:

> On 03.02.11 19:54, Paul Koning wrote:
>> What you need is the analog of zone.tab but with the bounding
>> polygon for each zone rather than a point inside it.  I believe that
>> data exists somewhere, but I don't remember the location.
> 
> If you do remember, PLEASE let me know. I have been dreaming about this since years.

To quote Paw Nielsen's message:

> For mapping lon/lats to timezones I use the maps that can be downloaded
> from this location:
> http://efele.net/maps/tz/world/
> 
> Just bear in mind the maps do not cover sea lon/lat's only land.

As for the sea, the tz-link.htm file in the tzcode distribution says

	• A ship within the territorial waters of any nation uses that nation's time. In international waters, time zone boundaries are meridians 15° apart, except that UTC−12 and UTC+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.