السلام عليكم ورحمة الله وبركاته when does combining and shortening the prayer begin for the traveler?

Imam Ibn Baz mentioned: If he departs from the city and exits its inhabited and built-up area, going to the airport which lies outside the city, or he travels in his car outside the city, he prays two rak‘ahs. However, as long as he remains within the city, he prays four. When he leaves the city and goes beyond its structures and habitation, he then prays two rak‘ahs on his way to the place he intends.