A long time ago, I posted some code and information about how to add GeoURL information to your journal.
Those instructions are no longer even remotely neccesary, as LiveJournal now supports the ability to set your location via the admin console.
Visit the admin console, and type something like:
set icbm "34.2234,-122.3434"
set icbm "34.23234N 122.3432W"
This results in a tag similar to <meta name="ICBM" content="34.2234,-122.3434" />
If you're in the US, you can look up your latitude and longitude using geocoder.us. If you're outside the US, you can search for your address on Google Maps. Once you've found it, double click slightly away from the marker, and click "link to this page". The URL in the browser bar now contains something like: "ll=41.85,-87.65". Copy paste the bit after the "ll=" and before the next &, and paste that into the admin console command above.
Then you can Ping GeoURL and see your neighbors. (Hello, Cambridge!)