I travel frequently and have friends scattered throughout the country. I usually do a bad job of keeping track of who is where, who has moved, etc.

Last week I was in Boston. As I headed out to dinner, I updated my Facebook status:

Later that night, I got a Facebook message from a friend I haven’t seen since high school. He lives in Cambridge and wanted to get together.

Unfortunately, the message arrived after I had gotten back to my hotel.

This almost-connection was facilitated by Facebook’s social graph and status updates. Next time I’m in Boston, I know to look Chike up. Twitter, Jaiku (acquired by Google) and Pownce can be used in the same way. But none of them know geography; they require that someone look at the message and determine that Cambridge is nearby. A friend who lives in Los Angeles is just as likely to see that message as someone in Cambridge.

There are a number of companies trying to turn that missed connection into an actual connection. Among them are Loopt, uLocate and Whrrl. Google purchased a pioneer in the field — Dodgeball — but hasn’t done much with it. (Dodgeball’s founders very publicly left Google, complaining that they couldn’t get engineering resources.)

Although the details vary based on site, you can publish your location from the Web or a cell phone. You can also see where your friends are on a map. I could have checked a map before I headed to Cambridge to see which of my friends were nearby. Some services will even alert you when a friend is nearby.

More on: location-based services, maps

Disclosure: I have a consulting relationship with uLocate.