It is actually relatively easy to tell where the city proper ends and outskirts begin as Arrakeen is corralled by Harkonnen guard posts and some walled sections, though for a single person with a modicum of stealth it is not difficult to pass in and out unnoticed.

The area outside is dominated by water farms and storage areas, with an occasional manufacturing facility, of which spice refineries are the dominant ones, or a richer household. The roads are wide and accessible for ground transport.

Still, toward the Old Gap in the Shield Wall, a high pass to the open desert, there is a fluid shantytown of tents for all those who can't or wouldn't live in Arrakeen but have business there. That usually means the desert folk. Its size ebbs and flows, depending on the prospect of a Harkonnen pogrom. Right now it is rather small, as Glossu Rabban is in the midst of his campaign against the Fremen and the tents are regularly raided in pursuit of infiltrators.