The accuracy of mapping derived from the General Land Office surveys: : presettlement wetlands and deepwater habitats within Lake County, Illinois
Paulson, Lisa M.
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The accuracy of mapping derived from of General Land Office survey (GLO) data for a portion of Lake County, Illinois is assessed. This study is based upon similar research conducted by Iverson and Risser in 1987. Due to the coarseness of the original surveying grid, the proportions of wetland and deepwater land cover are believed to be under-represented in GLO data. This study compares the wetland and deepwater habitat proportions within the Antioch 7.5-minute quadrangle. The wetland and deepwater habitats for GLO data are compared to the same categories of National Wetlands Inventory (NWI). Land Use and Land Cover (LU/LC) data are also assessed. A difference of proportions analysis was conducted on all three data bases (GLO, NWI, LU/LC). With respect to the GLO data, the results of the analysis were different than what was originally hypothesized. There is insufficient evidence to conclude that the GLO data are biased. Comparison with the NWI and LU/LC data corroborates the conclusion of no bias present within the GLO data. When compilation methods of the GLO data are considered, it is not surprising that there is no bias found. The enhancement of Lake County's GLO map with natural resource information brought the resolution of the NWI and the GLO data closer together. Because the NWI and GLO data are now systematically similar, and no bias was found within the NWI data, we can conclude that there is no bias within the GLO data. Land Use and Land Cover data were analyzed to determine if the results of this study would concur with the results of the same data of the Iverson and Risser 1987 study. The results of this study did agree with those of the 1987 study.