A good design for the city is usually pleasing, healthful and harmonious to people. In order to achieve the goal, urban planners must follow many rules from math. For example, the urban web will be at its best when it is multiple and irregular; in mathematics, there is a theorem which says that two points can only be connected in one way by a straight line, but in infinite ways by curved lines. Therefore, in order to increase the number of connections between points, curved connections must be used.
A principle of physics states that the interaction between two objects can be written as the sum of interactions over all possible paths between them. Basically, the mathematical theory of the urban web is structurally based upon three principles: nodes, connections, and hierarchy.
Geometry is in our everyday life, it can be almost everything we see; geometry plays a huge part in urban planning. The appearances of the cities, the streets, the squares, can easily seem as the mirror of its society. For example, a city with plenty of space can make people feel it's huge and relaxing, but also empty. On the other hand, a smaller city with less space, where there's not many main streets but only alleyways, can make people feel close and warm, but sometimes crowded. With different geometrical designs of the cities or the buildings, the level of convenience will also be different.
This page by Tim C.