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Improved Urban Maps for the United States

This article is a part of the Fall 2019 issue of the Earth Science Matters Newsletter.

Monitoring and understanding land-use change in America is critical given our continued growth, urbanization, and dependence on natural resources. To achieve more accurate assessments of urban land changes, USGS scientists from the Patterns in the Landscape – Analyses of Cause and Effect (PLACE) team employed two decades of satellite data to interpret and study landscape change across the conterminous United States from 1992-2011.

Beginning in 2015, a small group of geographers came together to improve United States urban land maps by making adjustments to multidecadal, national-scale land-use maps produced by the National Land Cover Database (NLCD). NLCD has been the seminal source for wall-to-wall land-use/land-cover maps of the country, and part of the NLCD effort centers on mapping developed lands. Existing change estimates generated by NLCD and others covering the 1990s and early 2000s represent the best available data for land managers and other researchers, but uncertainties remained.

Early in their exploratory effort, the PLACE team determined that rural roads included in the developed classes of NLCD maps were problematic due to inconsistencies in road location, density, and continuity. In addition, some classification techniques associated with rural areas and impervious surfaces contributed to artificial increases in areas classified as developed. To mitigate these challenges, scientists hypothesized that a series of post-processing techniques could effectively improve the NLCD maps spanning the years 1992-2011. The team edited and removed rural roads in the NLCD developed class by intersecting a suite of geospatial land use data and manually removing misclassified areas. Their efforts resulted in higher accuracy maps of urban land and improved urban change estimates spanning a 19-year period.

The removal of roughly 230,000 square kilometers of rural roads from the NLCD developed class resulted in maps that better characterize the urban footprint, with a national accuracy approaching 99 percent in 2001 and 2006. These urban maps provide improved inputs for modeling applications and policy decisions that rely on quantitative and spatially explicit information regarding urban lands.

Examples of before and after maps for urban areas of Houston, TX and Wichita, KS are shown in Figure 1. Since their publication, the revised maps have been used in peer-reviewed land-use forecasting efforts and by the NLCD team to help develop its 2016 land-use/land-cover map. Additionally, USGS researchers are actively using these data to develop annualized urban maps for California to further refine our communal understanding of contemporary land use changes in the West.

before and after rural road removal maps
Figure 1. Comparisons between NLCD developed class (left panel) and the new urban maps (right panel) for Houston, TX (upper) and Wichita, KS (lower). (from Figure 5 in Soulard et al., 2018)

By creating novel protocols to improve existing land cover data, the resulting maps contribute to an improved national urban map repository. These efforts advance our understanding of the rates and causes of land change in the United States while helping managers and stakeholders make more informed decisions to better prepare for the future.

The paper, “Removing Rural Roads from the National Land Cover Database to Create Improved Urban Maps for the United States, 1992 to 2011”, was published in Photogrammetric Engineering & Remote Sensing and was recognized as the third-place recipient of the 2019 ESRI Award for Best Scientific Paper in Geographic Information Systems. It is available at: https://pubs.er.usgs.gov/publication/70195240. Geospatial data are also available at: https://doi.org/10.5066/F79G5K05.

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