Thinking about maps, and latitude/longitude in the context of Protest.net, and calculating applicability. (e.g., it would be nice to be able to show all the upcoming events in a 50 mile radius).

Key terms to search for are geocoding, and gis. There is a fairly high availability of the TIGER 2000 Census data for the US for converting zip codes into lat/long, that is however, very inaccurate. Unfortunately the more detailed Zip+4 data is not freely available. (though what business the Post Office, or the Census Bureau has capitlizing on that data is unclear)

The online map vendors take it to the next level, making guesstimates based on the street by street basis. It should be possible to us those same techniques with the TIGER database.

Guide to Mostly On-Line and Mostly Free U.S. Geospatial and Attribute Data seems popular.

Daniel Egnor’s geographic search won the Google programming contest.

None of this stuff is international, or particularily satisfying. I failed to find a real active open source community around this, which I think speaks to the lak of good data, and a lack of itches to scratch. Hopefully the new abundance of GPS info, and the sexiness of war-driving will change this.