Would it be possible to have a category field added to the site object. Eg Technology, Culture, etc. The sites seem to already have categories, as you can see on this page: https://stackexchange.com/newsletters. (although it seems few sites aren't on that page?)
Categories aren't sufficiently stable to expose in the API.
It is entirely possible (even likely, in my opinion) that we'll revisit and rework the proposal categorization significantly in the coming year.
1So they will be put in later when they've been revisited. It's quite unwieldy to present the user with such a long list of sites. Jan 31, 2012 at 19:45
2@Jonathan. - If they're stable and we're happy with them, not really true in either case with Area 51 categories at the moment. I see the need for something like them, but don't have anything I'm comfortable making part of a contract at the moment basically. Jan 31, 2012 at 19:47