A residential area is a land use in which housing predominates, as opposed to industrial and commercial areas. Housing may vary significantly between, and through, residential areas. These include single-family housing, multi-family residential, or mobile homes. Zoning for residential use may permit some services or work opportunities or may totally exclude business and industry. It may permit high density land use or only permit low density uses. Residential zoning usually includes a smaller FAR (floor area ratio) than business, commercial or industrial/manufacturing zoning. The area may be large or small. In certain residential areas, largely rural, large tracts of land may have no services whatever, thus residents seeking services must use a motor vehicle or other transport, so the need for transport has resulted in land development following existing or planned transport infrastructure such as rail and road. Development patterns may be regulated by restrictive covenants contained in the deeds to the properties in the development, and may also result from or be reinforced by zoning. Restrictive covenants are not easily changed when the agreement of all property owners (many of whom may not live in the area) is required. The area so restricted may be large or small. Residential areas may be subcategorized in the Concentric zone model and other schemes of urban geography.