lat/lon to time offset database

Jonathan Stott jonathan at
Thu Feb 3 23:16:58 UTC 2011

On 03/02/2011 18:33, Larry Ober wrote:
> I'm a nubie at understanding the ins and outs of timezones so please forgive
> me for my potentially dumb questions.
> 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".

I had a go at doing this a few years ago when I was creating the website. I thought like you that it would be fairly 
straightforward, but no, it's really not! The result is accessed by 
webservice through, but the data is a few years old now 
and it's not really that accurate.

I basically generated a map of the zones as accurately as I could 
(limited by not having accurate administrative area boundaries) and did 
some processing to reduce the complexity of lookups. I blogged about it 
5 years ago: and

If anyone has any ideas for how to improve the accuracy or, more 
importantly, map daylight savings time rules (which are even more 
complicated), I'd love to know!


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