Source: Dr. Jean-Paul Rodrigue, Hofstra University Campus GIS, 2015.
Land use can be defined using different classification criteria. While formal land use refers to the qualitative attributes of space, functional land use indicates its socioeconomic function. For instance, while factory is a qualitative attribute, industrial is an economic function. The above maps represent the land uses of the same neighborhood, classified formally (left) and functionally (right). Under such circumstances, land use that has been formally classified as built up can be functionally described as residential, commercial, institutional, or industrial.
The formal land use map can be created with aerial or remote sensing images, but it is very difficult to infer any functional attributes from these observations, especially for urban land use. An aerial photo of a building reveals little about its function, although a trained observer would be able to infer residential and commercial uses with a reasonable level of accuracy by considering attributes such as size, height, and parking space. For agricultural land, remote sensing images have been proven to be efficient tools for functional land use classification as it is possible to identify the nature of the vegetation (forests, grazing land, crops, etc.) from its electromagnetic signature. Such attempts for urban areas have proven excessively difficult, especially in high-density zones.
The functional land use map requires an implicit knowledge of the functional attributes of an area, commonly gained through field observations or censuses. The great majority of city planning agencies have undertaken surveys to assess the functional attributes of land use under their jurisdiction. Such an endeavor is often time-consuming as the urban landscape is a constant state of change with the construction/renovation of infrastructures, new residential/commercial/industrial developments, and the modification of existing uses.