A city block, urban block or simply block is a central element of urban planning and urban design. A city block is the smallest area that is surrounded by streets.
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 land lots 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 space. Most cities are composed of a greater or lesser variety of sizes and shapes of 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. In most cities of the world that were planned, rather than developing gradually over a long period of time, streets are typically laid out on a grid plan, so that city blocks are square or rectangular.