While you are at it make sure you have a decent android device so you can test on hardware. Once you have put the time in to test your idea (40-100hours) you should have a pretty good idea if you want to continue with it. Just because there are ideas and apps that do this does not mean you cannot build something better or more streamlined.
Is the idea to network with people who live nearby? There are already apps that do that (e.g. NextDoor). Any app can be made given enough programming knowledge or money. The real question is "should it be built?"
Exercise for the enthusiast - work out how your proposed product could be used by a stalker or abuser. I, for one, wouldn't go anywhere near a Facebook/Maps mashup.
First step is to learn how to develop android apps.
Read all of this developmenthttps://developer.android.com/training/basics/firstapp/
Learn about Google Maps https://developers.google.com/maps/documentation/android-sdk...
Learn about integrating with facebook https://developers.facebook.com/docs/android/getting-started...
While you are at it make sure you have a decent android device so you can test on hardware. Once you have put the time in to test your idea (40-100hours) you should have a pretty good idea if you want to continue with it. Just because there are ideas and apps that do this does not mean you cannot build something better or more streamlined.