Facebook is using a new “Which city do you live in?” sidebar module to prompt users to list more personal information in their profile. The module suggests a city based on a user’s other data and connections, and allows them to add that city to their profile with a single click. Current city is one of the most valuable pieces of data to advertisers because permits location-specific ad targeting. Since Facebook sell access to this data in an anonymized form, pushing users to list their current city assists Facebook’s monetization efforts.

The current city ad targeting parameter is Facebook’s biggest money maker. It’s crucial to ads run extensively by restaurants, contractors, and group deals providers like Groupon that make up a significant portion the performance ad revenues that fund the company. The more data points and the higher the accuracy of this information, the more advertisers who will shift spend to Facebook in order to target these users and the more Facebook can charge them.

Users who haven’t listed their curent city in their profile may see the right sidebar module while browsing areas of the site such as Events. The module suggests a possible city and shows a link and picture of its community Page, as well as either a friend who lives there or the number of people who Like that Page. The suggestions appear to be inferred from the cities of a user’s friends, and the location of their school, work place, and home town if they’ve provided that information.

Users can click “I live here” to instantly add the suggested city to their profile without leaving the currently viewed page, or click “Choose another city” to go to the profile editor and select manually. If a user clicks the ‘x’ button, the module disappears.

The December profile redesign also goaded users to list additional personal information, but in a more natural way. Providing this information improves the Facebook experience for users because potential friends can find them more easily, and the ads they see will be more relevant. Still, the direct appeal is clearly in the interest of Facebook’s bottom line. Users may be less inclined to add information if they realize the motive behind the request, and Facebook might therefore want to be more subtle.

[Thanks to Brittany Darwell for the tip.]