The purpose of the ClusterMap is to indicate where your Livejournal friends are concentrated, and possibly also to find other Livejournallers in your vicinity.

Livejournallers who visit this site are encouraged to add their location to the database - they will then be able to access a map showing the location of everyone on their friend list and their friend-of list who is in the database. Asking your friends to add themselves will provide a better map for you, as well as a map for them - likely already partially occupied.