Carneros Watershed: Map of Soil Erodibility Index

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Carneros Watershed: Soil Erodibility Index Map


  • Original source of data: SSURGO
  • Data analysis: Kathy Pugh and Fred Watson
  • Map produced by: Kathy Pugh
  • Map produced using: ArcMap
  • Coordinate system: Geographic Coordinate System - GCS_North_American_1983
  • Datum: D_North_American_1983

Data Analysis Steps Taken

  1. Download SSURGO data
  2. Receive zip file of zip files, each one like
  3. Extract, and open basic shapefile of map-units (MU): soilmu_a_ca069.shp in Arc
  4. Can't read tables in this zip, because need special MS Access Template
  5. Download Access template from
  6. Open template in Access; Enable Macros; and it should prompt for location of your tables
  7. Wait a few minutes while Access imports your tables
  8. Create some custom queries in Access to extract some kind of Kf for each map unit
    1. Review the SSURGO data model:
    2. Each MapUnit contains several Components, each containing several Horizons.
    3. First query selects the surface horizons:
    4. - it joins tables muaggatt+component+chorizon,
    5. - joining on keys mukey and cokey
    6. - selecting only horizons whose hzdept_r is 0 (i.e. surface horizons)
    7. - includes the kffact (Kf-factor) and comppct_r (Percentage of map-unit occupied by Component) fields that will be used below
    8. Second query takes first as input, and is a MakeTable query, making the table that will be used in Arc
    9. - computes an expression 'yournamekf: Sum([comppct_r]*[kffact]/100)'
    10. - it is a Summation query, and the Summation is done on the yournamekf field (above)
    11. - the other two fields are musym and mukey, and they are GroupBy fields
    12. Run the second query; it will make a table
    13. Export the table to DBF format (one way of getting it to Arc)
  9. Back in Arc, add the DBF table as a layer
  10. Join the soilmu_a_ca069.shp layer to the DBF layer, using the mukey
  11. Change the soilmu_a_ca069.shp symbology to display quantitative based on the yournamekf field

Alternate versions

  • None