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A city block, residential block, urban block, or simply block is a central element of urban planning and urban design.
In a city with a Grid plan, the block is the smallest group of buildings that is surrounded by . City blocks are the space for buildings within the street pattern of a city, and form the basic unit of a city's urban fabric. City blocks may be subdivided into any number of smaller usually in private ownership, though in some cases, it may be other forms of tenure. City blocks are usually built-up to varying degrees and thus form the physical containers, or "streetwalls," of public spaces. Most cities are composed of a greater or lesser variety of sizes and shapes of an urban block. For example, many pre-industrial cores of cities in Europe, Asia, and the Middle East tend to have irregularly shaped street patterns and urban blocks, while cities based on grids have much more regular arrangements.
By extension, the word "block" is an important informal unit of length equal to the distance between two streets of a street grid.
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. Oblong blocks range considerably in width and length. The standard block in Manhattan is about . In Chicago, a typical city block is , cityofchicago.org meaning that 16 east-west blocks or 8 north-south blocks measure one mile, which has been adopted by other US cities. In much of the United States and Canada, the addresses follow a block and lot number system, in which each block of a street is allotted 100 building numbers. The blocks in central Melbourne, Australia, are also , formed by splitting the square blocks in an Hoddle Grid with a narrow street down the middle.
Many Old World cities have grown by accretion over time rather than being planned, making rectangular city blocks uncommon in the innermost development among most European cities, for example. Exceptions include cities that were founded as Roman military settlements, often preserving the original grid layout around two main orthogonal axes (such as Turin, Italy); and cities heavily damaged during World War II (like Frankfurt). Following the example of Philadelphia, New York City adopted the Commissioners' Plan of 1811 for a more extensive grid plan.
Superblocks can also contain an orthogonal internal road network, including those based on a grid plan or quasi-grid plan. That typology is prevalent in Japan and China, for example. Chen defines the supergrid and superblock urban morphology in that context as follows:
"The Supergrid is a large-scale net of wide roads that defines a series of cells or Superblocks, each containing a network of narrower streets."Superblocks can also be retroactively superimposed on pre-existing grid plan by changing the traffic rules and streetscape of internal streets within the superblock, as in the case of Barcelona's superilles (Catalan language for superblocks). Each superilla has nine city blocks, with speed limits on the internal roads slowed to , through traffic disallowed, and through travel possible only on the perimeter roads.
A block without sidewalks is always within a block with sidewalks. The geometric subtraction of a block without sidewalks from block with sidewalks, contains the sidewalk, the alley, and any other non-lot sub-structure.
Since there is no standard dimension for city blocks, and they are typically rectangular in shape, meaning a block in one direction is a different length than a block in another, colloquial directions involving blocks as proxies for measurements in feet or meters can be both imprecise and relative.
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