TIA estimates from land use are made by identifying land use categories for large blocks of land, summing the total area of each category, and multiplying each area by a characteristic TIA coefficient. Land use categories commonly are used to estimate TIA because areas with a common land use can be identified from field studies, from maps, from planning and zoning information, and from remote imagery. Land use coefficient methods commonly are used because planning and zoning maps that identify similar areas are, increasingly, available in GIS formats. Also, land use methods are selected to estimate potential effects of future development on TIA with planning maps that quantify projected changes in land use. There are substantial differences in actual and estimated TIA estimates from different studies in the literature. Terms like low density and high density may differ in different areas. A residential density of one-half acre per house may be classified as high density in a rural area, medium density in a suburban area, and low density in an urban area. Granato (2010) provides a table with TIA values for different land-use categories from 30 studies in the literature.