This Digital Terrain Model (DTM) data was produced all or in part from LiDAR information as of 2015. The LiDAR derived DTM covers Washington County, Illinois and include inland streams, rivers, lakes ponds and tidal features. These data are appropriate for use in local and regional analysis. This data set has a vertical accuracy of 6.24 centimeters RMSEz, horizontal accuracy of 0.6 meters and point spacing of 0.89 meters. Digital Elevation Models (including terrain and surface models) are raster data sets created from whole LiDAR point cloud data sets (LAS files). The LAS files are the standard LiDAR file format which contains the raw point cloud data, these data are normally classified and distinguished between points on the ground, water or elevated features such as buildings, trees, towers, bridges, etc.. These LAS files are processed into elevation models to create gridded rasters. The first returns can be used to map the top reflective surface (Digital Surface Models - DSM), these normally include open terrain areas, as well as the tops of buildings, trees, towers, and other features elevated above the bare earth. The last returns are used to map the bare-earth terrain (Digital Terrain Models - DTM), these are normally produced with irregularly-spaced points rather than the uniform grid structure of a Digital Elevation Model (DEM), Digital Terrain Models will often include breaklines to help define edges of water bodies.