One of my hobby projects is building a tourist map of Tokyo. I started out with displaying a RSS feed from Google Maps on my own hand-drawn map of Tokyo. Even though the Google Maps API now allows custom coloring of your map, I still think google’s maps are overpopulated with information and are visually not very inspiring.
Having the system in place for placing geo data on my own map, I realized it should be just as easy to display twitter messages, as long as they include geo data:

Retrieving twitter messages with geo data from http://search.twitter.com/ starts with including a geo location in your search parameters (in this case ‘tokyo’). Still, many twitter messages include geo data that only includes a town and no latitude/longitude information.
For this map, I retrieve 60 messages that were twittered in Tokyo, and then filter out all the messages that actually have a latitude/longitude. When using a map of an entire country you’d get a lot more twitter results so that’s going to be the next step in this project!
Check out the beta version here:
http://www.eerkmans.nl/map