United States Department of Agriculture
Natural Resources Conservation Service		 Illinois Go to Accessibility Information
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Color Compilation and
Scanning of Soil Maps

Standard SSURGO compilation procedures:

Source documents for digitization of soil surveys usually consist of separate mylar overlays of soil polygons and special features. These overlays are pin-registered to mylar orthophotos, tics are drafted at quad corners, and features are delineated using film lead or ink. Labels are drafted with colors that scanners do not capture. The mylar separates are scanned, vectorized and attributed.

Benefits of standard method:

  • Source document can be efficiently scanned and processed

    • Drawbacks of standard method:

  • Accuracy varies with tic placement among overlays
  • Overlay adds an extra layer for introduction of error, e.g. shifts and bubbles
  • Soil scientists get burdened with the multiple layers used in compilation, introducing error
  • Error is introduced if overlays are developed by tracing lines from soils compiled directly onto orthophotos

    • Color compilation onto orthophoto:

    Soil scientists are comfortable compiling directly to base maps. The best digital soil map would be one that is directly compiled to, and captured from the base map. DuPage and Fulton Counties, Illinois were compiled with this premise in mind. Half-tone, orthophoto quarter quadrangles were used as base maps. Soil polygons were compiled with 0.5 and 0.7mm red colored pencil. Special features were compiled using orange colored pencil. Although not part of SSURGO, hydrography was compiled using 0.5 and 0.7mm blue colored pencil. 3.75' tics were drafted using red colored pencil.

    Color scanning:

    Sheets were scanned by Scantech, Inc, Champaign, Illinois using a Crosfield drum scanner at an approximate resolution of 300 dots per inch. Resulting multi-band TIFF files were color separated using Adobe PhotoShop. Three binary TIFF files were produced for the red, orange and blue separates.

    Sample of grey scale image of scan

    Sample of grey scale image of scan

    Sample of composite of grey scale band and red band

    Sample of composite of grey scale band and red band

    Raster to vector processing:

    TIFF files of color separates were successfully processed by AverStar Geospatial, Inc, Portland, Oregon using LT4X software.

    Sample of soil vector lines overlain on composite of grey scale band and red band

    Sample of soil vector lines overlain on composite of grey scale band and red band

    Our findings

  • This method streamlines the work of recompilation for soil scientists
  • This is a direct method, which minimizes error. The more something is handled, or is separated from the source, the greater the chance for introduction of error
  • High quality scanners and operators are required to get satisfactory color separation
  • The data conversion contractor was completely satisfied with the raster source files
  • This method is more expensive (~2X) than creating quality overlays
  • Orthophotos must be matte film mylar

    • The future

  • The typical orthophoto currently provided is clear film mylar, which can't be drawn on
  • The advent of digitizing centers and state funding will limit further use of this method by us, however, every opportunity we have to pursue direct conversion will be investigated

    • For More Information Contact:

    Tom D'Avello and Bob McLeese