If you're in a committed relationship, you might be planning a candle-lit dinner tonight with your beloved. If you're single, on the other hand, you might be thinking about how to find that special someone.

Facebook is here to help. The social networking giant has what might be the world's largest dataset on love and relationships, generated by hundreds of millions of users telling Facebook about their relationship status, geographic location and much more.

You might think that your odds of finding love are higher if you're around a lot of other single people. But Facebook finds just the opposite: Single people couple up faster in places where most people are already in relationships.

Washington, D.C., New York, San Francisco and Los Angeles are awash in single people. And evidently, many of them like it that way. These cities have among the lowest rates of relationship formation. In contrast, Salt Lake City, Colorado Springs  and Portland, Ore., have few single people, and relationships form quickly there.