Transportation is an act of getting people or goods from one place to another. Without transportation, there would be no trade and without trade there would be no towns or cities, which are the centers of civilization. There are 3 types of transportation: land transportation depends on vehicles with wheels, water transportation depends on ships, and air transportation includes airplanes which can be passenger, transportation, or private, where the pilots operate their own vehicles. People travel mostly by cars. There are public taxi services which operate on a passenger per mile fee basis. Public transportation is where people pay to ride in vehicles operated by companies. In urban areas, this is called mass transit. For people who don´t own a car or don´t like driving in the city, the mass transit between cities and their suburbs is called commuter service and consists mostly of buses and trains. There is intercity transport between cities consisting of airplanes, buses, and trains. Overseas transport consists mostly of airplanes and previously ships (now used only by Queen Elizabeth II).