So, it’s my turn to write something here again. Ho-hum. Anyway, lately I’ve been working on adding the geographical features to PledgeBank which everyone thinks are there already: specifically, finding pledges which are nearby. To start with, we’re doing this for the UK only (because we already have the infrastructure to do postcode-to-coordinates lookups through MaPit), but the intention is to do thiis for the whole world as soon as we can, either by having users select their location through a gazetteer, or, where we can get the data, by using a similar postcode/zip-code/whatever-to-coordinates lookup. So that means we have to deal with places which might be anywhere on earth, which means dealing with latitudes and longitudes. And as anyone who’s dealt with this stuff knows, it’s very tedious to get this right. I’m afraid I’ve now spent too long reading about datum ellipsoids and Helmert Transforms to want to spend any time at all talking about them, so in the unlikely event that you’re interested, you’ll just have to read the (relevant parts of) code.
Oh, and if anybody has good suggestions for a hierarchical gazetteer with world-wide coverage, I’d love to hear them. Similarly, does anybody know if this one is any good?