“Drainage class (natural)” refers to the frequency and duration of wet periods under conditions similar to those under which the soil formed. Alterations of the water regime by human activities, either through drainage or irrigation, are not a consideration unless they have significantly changed the morphology of the soil. Seven classes of natural soil drainage are recognized-excessively drained, somewhat excessively drained, well drained, moderately well drained, somewhat poorly drained, poorly drained, and very poorly drained. These classes are defined in the “Soil Survey Manual.”
The rasters originate from the Gridded SSURGO (gSSURGO) database, a National Cooperative Soil Survey (NCSS) SSURGO product in the format of an Environmental Systems Research Institute, Inc. (ESRI®) file geodatabase. Both SSURGO and gSSURGO are considered products of the NCSS partnership. SSURGO generally has the most detailed level of soil geographic data developed by the NCSS in accordance with NCSS mapping standards (1:15,840 scale) and is stored in a vector format which display soil map unit delineations. The gSSURGO product was generated by creating a 10-m resolution raster of the original SSURGO vector data. The soil property tabular data are stored in the National Soil Information System (NASIS) database.
The zip file contains the base GeoTIFF soil property rasters, OVR pyramid files (reduced resolution for faster display), AUX auxiliary files (Raster color map, statistics, histogram, table, pointer to pyramid file, coordinate system, transformation, projection information), TFW world files (GeoTIFF coordinate system information), and a LYRX file (stored symbology for viewing in ArcGIS Pro v 2.2 or later) and a LYR file (stored symbology for viewing in ArcGIS for Desktop), and associated metadata in a RTF file.
Metadata – Sources – Limitations
Produced by: Meyer Bohn, Joshua McDanel, and Bradley Miller January (2019)
Created with the gSSURGO mapping toolset for ArcGIS for Desktop 10.6. Available for download at:
Raster Format: 10-m resolution GeoTIFF, 32-bit floating point
Projection: NAD83 UTM Zone 15N
Extent – West: -96.801571 East: -90.007463 North: 43.644364 South: 40.302683
Soil Survey Staff. 2018. Natural Resources Conservation Service. United States Department of Agriculture. Gridded Soil Survey Geographic (gSSURGO) Database for Iowa. Accessed 27 Oct 2018.
Use limitations: See “Sources of Apparent Error on Existing Soil Maps”. Soil Survey Staff. 2018. Soil Survey Manual – Ch. 4: Soil Mapping Concepts. Natural Resources Conservation Service. United States Department of Agriculture. Available at:
Scale Range: Not intended for use at scales larger than an order 2 Survey (1:12,000 to 1:31,680).