World Travel City Photography

Other forms may include a radial structure, in which main roads converge on a central point. This was often a historic form, the effect of successive growth over long time with concentric traces of town walls and citadels. In more recent history, such forms were supplemented by ring-roads that take traffic around the outskirts of a town. Many Dutch cities are structured this way: a central square surrounded by concentric canals. Every city expansion would imply a new circle (canals together with town walls). In cities such as Amsterdam, Haarlem, and also Moscow, this pattern is still clearly visible.
History
Towns and cities have a long history, although opinions vary on whether any particular ancient settlement can be considered to be a city. A city formed as central places of trade for the benefit of the members living in close proximity to others facilitates interaction of all kinds. These interactions generate both positive and negative externalities between others' actions. Benefits include reduced transport costs, exchange of ideas, sharing of natural resources, large local markets, and later in their development, amenities such as running water and sewage disposal. Possible costs would include higher rate of crime, higher mortality rates, higher cost of living, worse pollution, traffic and high commuting times. Cities will grow when the benefits of proximity between people and firms are higher than the cost.