<P> 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 . </P> <P> 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 . Using the perimeter block development principle, city blocks are developed so that buildings are located along the perimeter of the block, with entrances facing the street, and semi-private courtyards in the rear of the buildings . This arrangement is intended to provide good social interaction among people . </P> <P> 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 . However, as reference points, the standard square blocks of Portland, Houston, and Sacramento are 264 by 264 feet (80 m × 80 m), 330 by 330 feet (100 m × 100 m), and 410 by 410 feet (120 m × 120 m) respectively (to the street center line). Oblong blocks range considerably in width and length . The standard block in Manhattan is about 264 by 900 feet (80 m × 274 m); and in some U.S. cities standard blocks are as wide as 660 feet (200 m). The blocks in Calgary, Canada, are 330 by 560 feet (100 m × 170 m), while those in Edmonton, Canada are 197 by 560 feet (60 m × 171 m). The blocks in central Melbourne, Australia, are 330 by 660 feet (100 m × 200 m), formed by splitting the square blocks in an original grid with a narrow street down the middle . In Chicago, Illinois and Minneapolis, Minnesota, a typical city block is 660 by 330 feet (200 m × 100 m) (w × h), meaning that 16 east - west blocks or 8 north - south blocks measure one mile . </P> <P> Many world cities have grown by accretion over time rather than being planned from the outset . 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 . One notable example is Turin, Italy . Following the example of Philadelphia, New York City adopted the Commissioners' Plan of 1811 for a more extensive grid plan . By the middle of the 20th century, the adoption of the uniform, rectilinear block subsides almost completely and more picturesque layouts prevailed, with random sized and either curvilinear or non-orthogonal blocks and corresponding street patterns . </P>

What is the average distance of a city block
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