How does apps like foursquare or gowalla implement their check-in feature?

If I had to build my own check-in feature from scratc开发者_如何转开发h, how would I go about it? I was thinking that once a location is determined using corelocations, I can add that location co-ordinate and timestamp to a database in some server. Now once one of my friends check-in close to that location, there can be a query to the database to figure out all check-ins around that location and around that timestamp. Is that how they implement this feature?

Those services use the current location (that you could get via CoreLocation or otherwise) in order to determine which venues to show near the user. Note that they usually have a database of business venues and the user selects the one they are actually and perform the checkin.

So, in order to figure out "who you are hanging out with", they only have to see who has checked in in that specific location, around that timestamp.

Note that the whole thing could have been implemented without location services and geographical coordinates - just choose from a list! Now, with location services, you can help the user search for the place quickly.