For iOS the GPS chip itself is only turned on when 1) a foreground application is using location 2) a navigation app is using location and you task switch (that blue bar you get at the top) 3) for background location, when the device reassociates to a new cell tower
This isn't true, an app has to explicitly turn GPS hardware on. Almost all the time apps, foreground or background, get locations passively, which is done by triangulating cell tower positions, i.e. the location the phone already knows.