Quantifying change in urban land provides significant information to create empirical models examining the effects of human land use. Maps of developed land from the National Land Cover Database (NLCD) of the conterminous United States include rural roads in the developed land course and therefore overestimate the amount of urban land. To better map the urban course and understand how urban lands change over time,we removed rural roads and small patches of rural development from the NLCD developed course and created four wall-to-wall maps (1992, 2001, and 2006,and 2011) of urban land. Removing rural roads from the NLCD developed course involved a multi-step filtering process, data fusion using geospatial road and developed land data, and manual editing. Reference data classified as urban or not urban from a stratified random sample was used to assess the accuracy of the 2001 and 2006 urban and NLCD maps. The newly created urban maps had higher overall accuracy (98.7 percent) than the NLCD maps (96.2 percent). More importantly,the urban maps resulted in lower commission error of the urban course (23 percent versus 57 percent for the NLCD in 2006) with the trade-off of slightly inflated omission error (20 percent for the urban map, 16 percent for NLCD in 2006). The removal of approximately 230000 km2 of rural roads from the NLCD developed course resulted in maps that better characterize the urban footprint. These urban maps are more suited to modeling applications and policy decisions that rely on quantitative and spatially explicit information regarding urban lands.
Source: usgs.gov