Description: The purpose of this map is to provide a georeferenced characterization of vegetation in the early stages of Euro-American settlement. One of the research uses for the surveys nationally is for presettlement vegetation. This data can be used to analyze presettlement vegetation patterns for the purpose of determining natural community potential, productivity indexes, and patterns of natural disturbance. The area of the original plat maps were townships; use of the data at a larger scale would not be appropriate.In Illinois, the surveys began in 1804 and were largely completed by 1843. The surveyors moved across the state laying out a rectangular grid system, known as the Public Land Survey System (PLS or PLSS). They were required to keep field notebooks where they noted details about their survey (such as which kind of tree was 'blazed' or marked at the section corners), as well as notes about the quality of the landscape, mines, salt licks, watercourses, springs, mill seats and other 'remarkable and permanent things'. Once a township was finished, the surveyors were to make a map of the area. These surveys represent one of the earliest detailed maps for Illinois. They predate our county land ownership maps and atlases. These plat maps and field notebooks contain a wealth of information about what the landscape was like before the flood of settlers came into the state. Most of the over 1,700 townships in Illinois have at least one version of the original surveyor's map. Additional redrafted versions are also available for all townships. The redrafted versions were created in the 1850's at the regional GLO office in St. Louis, Missouri. Cartographers used the original maps in consultation with the field notebooks to create a more complete map of the township. It is these plat maps that the Illinois Natural History Survey used to create our Early 1800's land cover Land Cover map. The original GLO maps and field notes are housed in the Illinois State Archives in Springfield. Microfilm copies of the maps were made in the 1960's and distributed to several state university libraries and research centers across Illinois. We borrowed the set of microfilm housed in the Illinois State Geological Survey library. Each GLO map was scanned from the microfilm onto a laptop computer. We used Adobe Photoshop software and a Canon MS400 microfilm scanner to capture the images saving them as tiff files. The images were georectified, or spatially-referenced (using ERDAS Imagine software) against USGS Geological Survey Digital Raster Graphic (DRG) images (scanned USGS 7.5 minute topographic quadrangle maps) by matching the township and section corners on GLO images to the corresponding points on the DRG. This process allowed us to digitized or 'trace' the line work on the plat map using Geographic Information System (GIS) software (ESRI Arc/Info). Forty two different land cover categories and features from the plat maps were digitized. All land cover categories and feature names were the ones used by the surveyors or cartographers. The names of some features seemed to varied by area of the state (probably by surveyor) and were combined. These included bluff/sand bluff, barrens/open barrens, bottoms/bottom land, field/enclosure, hills/sandy hills, high ridge/sandy ridge, island/sandy island, mound/high mound, river/wide river, ravine/gully,valley/hollow, sandy prairie/sandy ground, timber/forest/grove/wooded. Towns and roads or trails were not digitized. The scanned, georectified images of each township are now a permanent archive of the GLO maps. This will allow users to view the original plat maps. The separate digitized version of the plat maps is a statewide GIS coverage, which can be used on its own or as a layer in GIS analysis. Five revisions of the data have been released. One correction was in the NW corner of present day Peoria County. The scanned township on the microfilm was mislabeled. The correct township was obtained and data was corrected. A second error was discovered in present day Adams county. A prairie area was mis-digitized and incorrectly labeled as forest. The missing lines were added and the labels were corrected. The third error set of errors included Massac and Lawrence counties. In Massac county, a pond was mis-labeled as a prairie. The label was corrected. In Lawrence county, along the Wabash river, stray lines were removed and ridge lines were added in the forest area. The forth-fifth set of errors included JoDaviess, Carroll and Stephenson counties. In JoDaviess county, a forest area was mis-labeled as prairie. The label was corrected. In Carrol county, a line between forest and prairie was missing. This line was added and incorrect lines were deleted. A prairie label was added to the resulting polygon. An adjacent forest larea was mis-labeled as prairie. This was corrected. In Stephenson county, several lines were removed. One line was added and several labels mis-identified as prairie were corrected to forest. The sixth set of corrections were made in Lake county. A color version of the plat maps were obtained and georeferenced, providing a clearer view of lines and labels. The primary changes were to ponds, streams, wetlands and bottomlands which were added or modified. This two-year effort was partially funded by Illinois Department of Natural Resources, Office of Realty and Environmental Planning.
Service Item Id: a9168d3d91e24986960536c80cf8b66b
Copyright Text: Illinois Natural History Survey, 2007