lat/lon time offset database

Hjwoudenberg hjwoudenberg at
Fri Feb 4 00:23:00 UTC 2011

For time zones I use ISO 3166 country codes and state codes.
For some states I need a suffix like 'n'  or 'w'  or 's' or 'e' if the state has more than one time zone.
It also can use the IATA city code, the 3 letter code on your airline luggage.
It contains the time zone rules so each year it calculates the new dates for daylight.
The rules can be updated on demand, when used first time each year, over the Internet. 
It also contains the ISO country name, state name and city name and airport name.
Hope fully the lat/lon for states and countries will someday be available even if they approximate coastlines. 
These should be a suggestion for the Unicode
CLDR Project
The Unicode CLDR provides key building blocks for software to support the world's languages, with the largest and most extensive standard repository of locale data available. This data is used by a wide spectrum of companies for their software internationalization and localization, adapting software to the conventions of different languages for such common software tasks as:
formatting of dates, times, and time zones, 
formatting numbers and currency values
sorting text
choosing languages or countries by name document describes the Unicode CLDR Technical Committee, and its process for data collection, resolution, public feedback and release. The process is designed to be light-weight: in particular, the meetings are frequent, short, and informal. Most of the work is by email or phone, with a database recording requested changes in data.
When gathering data for a region and language, it is important to have multiple sources for that data to produce the most widely acceptable data. Initial versions of data were based on the best available sources, but CLDR data will be modified and improved, in successive versions, by more input from the contributors inside and outside of the Unicode Consortium.
It is important to note that CLDR is a Repository, not a Registration. That is, contributors should not expect that their contributions will simply be adopted into the repository; instead, it will be vetted against the best available information.
Herman J Woudenberg

-----Original Message-----
From: Chris Walton <Chris.Walton at>
To: tz at <tz at>; larry.ober <larry.ober at>
Sent: Thu, Feb 3, 2011 5:37 pm
Subject: RE: lat/lon to time offset database

Just so you know that it is possible… some of the newer GPS units on the market today are capable of automatically determining the local time zone.
This is achieved with proprietary time zone maps that are installed inside the GPS at the factory.
Newer versions of the maps are bundled inside firmware images so that you automatically get the latest map when you upgrade the firmware on your GPS.
If these built in time zone maps are not accurate (or if you find yourself in an area with disputed time zones), it is possible to turn off automatic mode and then manually enter the time zone of your choosing.

A Google search reveals that one of the GPS manufacturers stores its time zone data in a file that is approximately 600kB.
I think we can assume that the data in this file is written in a very heavily compressed format; it could theoretically be many megabytes if uncompressed.
From: Larry Ober [mailto:larry.ober at] 
Sent: February 3, 2011 2:27 PM
To: tz at
Subject: Re: lat/lon to time offset database

Hi John,


Well there would be some level of accuracy question. The more accurate the polygon the larger the database. Also if the lat/lon data was provided by GPS, there is the question of signal availability.


Basically it just seems dumb that I need to tell my GPS what time zone it's in. LOL


Best Regards



----- Original Message ----- 

From: John Haxby 

To: tz at 

Sent: Thursday, February 03, 2011 1:54 PM

Subject: Re: lat/lon to time offset database


On 3 Feb 2011, at 18:33, Larry Ober wrote:

I am looking at building a small embedded system (No OS) that will require 
determining the local time from the lat/lon of a location. So basically I need 
lat/lon to time offset from "GMT".

Does that work?   I'm sure I can find places in Spain that are that are close to Lisbon than they are Madrid but being in Spain the timezone should be Europe/Madrid.  Also, when you're on going through the channel tunnel do you go from being closer to Paris than you are to London only when you've left Calais?  Or before you get to Dover?


Or have I got hold of the wrong end of the sti 

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