Hi all, thanks for your help, If it's okay, I'll answer to all of you in this one email.
I looked inside the download, and there seemed like nothing like a concise one to one mapping unfortunately.
Perhaps the "zone.tab" file distributed as part of tzdata would be useful. You could search for the country code in the first column, or search for nearby latitude/longitude in the second column, or both, and then display a menu of a few likely choices.
I don't think this is suitable, since many such as Canada have 6 time zones (okay I can live with that), but many famous states and cities aren't represented at all from what I can tell.
There is one at http://download.geonames.org/export/dump/ (by country, it's a lot of data).
Certainly. I only want the most famous places, something closer to around 100k-200k filesize at the most (as my calc is only around 300k itself). If it means I have to filter yet another stage, then so be it, but then I would need to hunt for a list of the '1000 most well known places' (or similar) in the world. So it looks like back to the drawing board. I appreciate the help, but I find it rather surprising that something like this doesn't already exist. Just to say something like "London 3pm in New York" sounds like a very common thing to want. You'd think a lot of people would find such a database very useful. Am I mistaken here?