It's really nice that there's an easy way to put coordinates on a diary feed and all, but as near as I can tell, there's no easy way to filter diaries by geography, at least on the site. What I did in an attempt to see what's available is learned how to use Yahoo Pipes, then created something for (very roughly) the Pacific Northwest:
http://pipes.yahoo.com/robla/openstreetmappnw

I believe you should be able to create a clone and edit it if you want to set up a feed for your area.