If you can see the field, you can tell it's not an airport (although you'd know much sooner if you had your charts or cockpit GPS out), and decide if you want t

If you can see the field, you can tell it's not an airport (although you'd know much sooner if you had your charts or cockpit GPS out), and decide if you want to land there anyway. If you can't see the field, your iPhone GPS isn't going to be nearly precise enough to let you land safely anyway, even if it was an airport.