lat/lon to time offset database

Larry Ober larry.ober at
Fri Feb 4 02:08:28 UTC 2011

Thanks Guy,



----- Original Message ----- 
From: "Guy Harris" <guy at>
To: <tz at>
Cc: "Larry Ober" <larry.ober at>
Sent: Thursday, February 03, 2011 2:41 PM
Subject: Re: lat/lon to time offset database

> On Feb 3, 2011, at 10:54 AM, Paul Koning wrote:
>> The file might seem like a starting point, but it isn't really; 
>> it just lists each of the zones with a single point in that zone.  What 
>> you need is the analog of 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.
> The tz-link.htm file I mentioned in my previous message has a section 
> "Time zone boundaries" that says:
> • TZ timezone maps contains a shapefile of the tz regions in the world.
> • Administrative Divisions of Countries ("Statoids") contains detailed 
> lists of tz-related zone subdivision data.
> • Time zone boundaries for multizone countries summarizes legal boundaries 
> between time zones within countries.
> •'s Free Maps and GIS Data includes a Manifold-format map of 
> world time zone boundaries distributed under the GPL.
> • The US Geological Survey's National Atlas of the United States publishes 
> the Time Zones of the United States in the public domain.
> • The GeoCommunity lists several commercial sources for International Time 
> Zones and Time Zone Data.
> • 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.
> The links for those are:
> - the "TZ timezone maps" link (mentioned in 
> another message); "shapefile" links to 
>, which describes what a shapefile 
> is
> - "Administrative Divisions of Countries 
> ("Statoids")
> - "Time zone boundaries 
> for multizone countries"
> - "'s Free Maps 
> and GIS Data", but that link no longer works
> - "Time Zones of the United 
> States"
> - "The GeoCommunity 
> lists several commercial sources for International Time Zones and Time 
> Zone Data."

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