Urban form refers to the spatial arrangement of buildings, streets, parks and other land uses within an urban area, as well as the social and economic activities that take place there. Urban structure describes the arrangement of different land uses. There are several models of urban development, including point development, linear development, radial development, and poly-nuclear development. Linear development forms cities that concentrate along major transportation routes like roads or rivers in a ribbon-like pattern. For example, Mumbai exhibits linear development along its transportation corridors. Poly-nuclear development involves strategically planning a network of interconnected cities and towns.