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Problem: 'Unique values' symbology incorrectly classifies fields with subtypes that use coded domains

Description

When working with Geodatabase data, ArcMap's 'Unique values' symbology method does not work properly when the value field has different coded-domains defined for each subtype. The following may happen:

  • Features may be incorrectly classified
  • The Unique values symbology dialog may show incorrect coded-domain descriptions.
  • The frequency counts displayed on the symbology tab of the layer properties dialog may be incorrect.

Cause

ArcMap’s 'Unique values layer' symbology method does not work properly if the value field has different coded domains defined for each subtype. In this scenario, ArcMap works with the coded domain descriptions from the first subtype for all features. In other words, regardless of which subtype the feature belongs to, the description will be read from the coded domain definition for the first subtype. Features will also be symbolized according to the first coded-domain definition.

Solution or Workaround

  1. Use the Unique values, many fields symbology method.
  2. Select your data's subtype field for the first value field.
  3. Select the the field with multiple coded domains (the original value field from above), for the second value field.
Note:
Keep in mind the 'Unique values, many fields' method generates symbology based on all the unique combinations of the first and second value fields. Consequently, if some subtypes in your data share a coded domain, you will need to aggregate some of the generated classes to obtain a list of unique coded domain values.  
To group unique values:
  1. Use the mouse to select values.
  2. Right-click and select Group Values from the popup menu.
[O-Image] Grouping unique values