In order to manufacture, mine, or research, a company must have buildings, and building may only be located in cities. Cities can be located on the surface of planets or moons, or they may be in orbit around a planet or moon. Some planets, such as Jupiter, are gas giants, with no discernable surface, and are therefore unsuitable for cities. Only "rocky" bodies, such as Earth, its moon, Mars, or Jupiter's moons may have cities. Each city has a latitude and longitude; these must be a multiple of ten. For example, Philadelphia's coordinates are latitude 40, longitude -70. In addition surface cities, each planet or moon may have one space station city in orbit. These cities are distinguished from surface cities because they have no coordinates.