2017 Cook County 1 ft. elevation contours forPLSS Township Area20. Data is derived from 2017 lidar. If you plan on downloading this dataset it is recommended to use the File Geodatabase option. The shapefile format may not work for larger datasets.Details about creating the one foot contours:The contours were processed by the Cook County GIS Department in order to add contour classifications as Index Contours (every 5 feet), Intermediate Contours (every 1 foot), Index Depression Contours, and Intermediate Depression Contours. To create the classification Cook County GIS used theIdentify Contourtool in ArcPro. The input was the contour feature and the 2017 DEM that was delivered along with the LiDAR data.Details about the LiDAR Acquisition:IL 4 County QL1 Lidar project called for the Planning, Acquisition, processing and derivative products of lidar data to be collected at a derived nominal pulse spacing (NPS) of 1 point every 0.35 meters. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base Lidar Specification, Version 1.2. The data was developed based on a horizontal projection/datum of NAD83 (2011), State Plane, U.S Survey Feet and vertical datum of NAVD88 (GEOID12B), U.S. Survey Feet. Lidar data was delivered as processed Classified LAS 1.4 files, formatted to 15,414 individual 2500 ft x 2500 ft tiles, as tiled Reflectance Imagery, and as tiled bare earth DEMs; all tiled to the same 2500 ft x 2500 ft schema.Ground Conditions: Lidar was collected April-May 2017, while no snow was on the ground and rivers were at or below normal levels. In order to post process the lidar data to meet task order specifications and meet ASPRS vertical accuracy guidelines, Ayers established a total of 66 ground control points that were used to calibrate the lidar to known ground locations established throughout the WI Kenosha-Racine Counties and IL 4 County QL1 project area. An additional 195 independent accuracy checkpoints, 116 in Bare Earth and Urban landcovers (116 NVA points), 79 in Tall Grass and Brushland/Low Trees categories (79 VVA points), were used to assess the vertical accuracy of the data. These checkpoints were not used to calibrate or post process the dataDetails about the DEM:To acquire detailed surface elevation data for use in conservation planning, design, research, floodplain mapping, dam safety assessments and elevation modeling, etc. Classified LAS files are used to show the manually reviewed bare earth surface. This allows the user to create Reflectance Images, Breaklines and Raster DEM. The purpose of these lidar data was to produce high accuracy 3D hydro-flattened Digital Elevation Model (DEM) with a 2 foot cell size. These raw lidar point cloud data were used to create classified lidar LAS files, Reflectance Images, 3D breaklines, 1 foot contours, and hydro-flattened DEMs as necessary.