Generally speaking a city is a relatively densely populated incorporated area, usually consisting of residential, industrial and business areas. A large percentage of a city is generally taken up by buildings, streets and parks. Waterways, lakes and parks are usually the only undeveloped areas within a city center.
In American English, at least, the center is called "downtown".
The geographies of cities are diverse. Often cities will either be coastal and have a harbor or be situated near a river - for economic reasons. river[?] and ocean transport in bygone days was (and in most cases still is) cheaper and more efficient than road transport.
Older European cities which have not been extensively rebuilt tend to have city centers where the streets are jumbled together, often seemingly without a structural plan. This is a hangover from a time when city planning included the idea that a confusingly winding street layout would confuse invading armies. Today this is usually perceived by tourists to be quaint and picturesque. Modern city planning has seen many different schemes for how a city should look. The most commonly seen pattern is the grid, almost a rule in the United States, and used for hundreds of years in China.
Cities have a long history, although opinions vary on whether any particular ancient settlement can be considered to be a city. The first true cities are sometimes considered to be large settlements where the inhabitants were no longer simply farmers of the surrounding area, but began to take on specialised occupations. By this definition, the first cities we know of were located in Mesopotamia, such as Ur, and along the Nile, the Indus Valley Civilisation and China. Before this time it was rare for settlements to reach significant size, although there were exceptions such as Jericho, Catalhoyuk and Mehrgarh.
During the European middle ages, a city was as much a political entity as a collection of houses. A city could often have its own legislature, and sometimes a city could be directly under the supervision of the monarch, circumventing local noblemen.
The Industrial Revolution led to the rise of the modern great cities. Prior to that, cities were trading centers, but their populations were in general relatively small. There were exceptions such as the ancient cities of Rome and Byzantium, and 17th-century London. With the Industrial Revolution, as national economies changed from agrarian to industrial, huge numbers of people migrated from rural communities into the cities.
Modern cities are known for creating their own microclimates. This is due to the large clustering of hard sufaces that heat up in sunlight and that channel rainwater[?] into underground ducts. As a result, city weather is often windier and cloudier than the weather in the surrounding countryside. Conversely, because these effects make cities warmer (urban heat shield) than the surrounding area, tornadoes tend to go around cities. Additionally towns can cause significant downstream weather effects.