For this reason, a regular pattern of even, square or rectangular city blocks is not so common among European cities, for example.

An exception is represented by those cities that were founded as Roman military settlements, and that often preserve the original grid layout around two main orthogonal axes. Following the example of Philadelphia, New York City adopted the Commissioners' Plan of 1811 for a more extensive grid plan.

Since the spacing of streets in grid plans varies so widely among cities, or even within cities, it is difficult to generalize about the size of a city block.

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Superblocks were popular during the early and mid-20th century, arising from modernist ideas in architecture and urban planning.

Planning in this era was based upon the distance and speed scales for the automobile and discounted the pedestrian and cyclist modes, as obsolete transportation vehicles.

The concept of city block can be generalized as a superblock or sub-block.

A one square km superblock sector in Milton Keynes framed by major roads on a grid configuration.

Superblocks can also be found in central city areas, where they are more often associated with institutional, educational, recreational and corporate rather than residential uses.

Urban planner Clarence Perry argued for use of superblocks and related ideas in his "neighborhood unit" plan, which aimed to organize space in a way that was more "pedestrian-friendly" and provided open plazas and other space for residents to socialize.

The addresses on this example 800 block are shown in black and the adjacent blocks are the 700 and 900 blocks. Avenues are shown in green with walkways shown in light gray from every lot to the street.

An alley shown in light gray runs lengthwise down the middle of the block. A city block, urban block or simply block is a central element of urban planning and urban design.

Most cities are composed of a greater or lesser variety of sizes and shapes of urban block.