Urban areas are characterized by high population density when compared to other areas
Areas that are located on the outskirts of cities or large urban areas but retain rural characteristics such as agricultural productions are generally considered as peri urban areas
One way would be to limit who can receive a passport or visa to travel to another country and another would be at the entrance to the country they may not be admitted for example due to inadequate funds to live. In my case, when I travelled by bus from Costa Rica to Panama, the Panamanian authorities required that I either have a ticket out of the country or a return ticket back to San Jose, Costa Rica.
Most of those major cities are located near Petroleum Fields and Coal Mines.
