XKCD has an amusing “map of online communities and related points of interest” in which “geographic area represents estimated size of membership”. The map cautions that it is not a complete survey and should not be used for navigation.

Related posts:

1. Akshay Java on Mining Social Media Communities and Content
2. Akshay Java Ph.D.: Mining Social Media Communities and Content
3. ISWC04 papers available online
4. Comparison of Online Social Networks in Terms of Structure and Evolution
5. Pew: 11% of online adults twitter and/or update status