More details have appeared about Facebook’s location plans: It will provide a way for you to share your location via your phone, and show you a list of nearby venues that you can check in to. That’s according to software code, below, that showed up in the version of the site designed for the iPhone mobile operating system, touch.facebook.com, as TechCrunch discovered yesterday.

This follows a long string of rumors and clues about the service. The most recent: McDonald’s is planning to include some form of check-in service in partnership with Facebook, AdAge reported last week, that would allow users to tell their friends when they go to one of the fast food chain’s locations.

The iPhone mobile site uses the location functionality available in the new HTML5 web markup language standard to get your location from your phone, showing you a new check-in part of the site called Places. Beyond latitude and longitude, the code also includes ways to record altitude, direction and speed — although these are generally part of the standards specification around what location data is shared, and won’t necessarily be included in whatever Facebook launches.

The code amounts to more evidence that Facebook will provide a way of checking in at physical locations, which hasn’t been entirely clear in the past. One can imagine a “check-in” appearing as a story in users’ news feeds, similar to a status update or anything else — and analogous to Foursquare and other location-driven games, like Foursquare, that use the check-in concept.

We continue to expect that Facebook will find other ways to integrate location into its platform, both giving location data to third parties and getting it from them.

Facebook could provide location in more general ways, though — perhaps some sort of geo-tag that gets included in a status update, as Twitter has done, for example. It already provides documentation for how developers can add location to their Pages as part of its Open Graph Protocol, as we wrote about last month. It’s not clear how this functionality will interoperate with check-ins. One way it could: Allow businesses to provide their own locations to appear in Places, especially in case people aren’t able to find the locations using their phone’s GPS.

Another clue for Facebook’s plans is that McDonald’s is providing the service through an application located in the tab of its Facebook Page, but not the Page itself. This suggests Facebook is enabling McDonald’s to access location information through an application API that it has yet to release.