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The union operation combines and preserves all features and corresponding attributes from a set of input feature class layers.

How the Union Operation Works

Access the tool from eRAMS GIS Tool > Geoprocessing > Feature Class > Overlay > Union

eRAMS GIS_Union_Toolbar


  • The operation creates polygons that are unique combinations of the features from input layers.
  • Union requires that both feature layers to be polygon layers.
  • The order of entries in the list of input feature layers does not affect the output layer spatial features or attributes.


  • The extent of the output layer is the combined extent of the input layers.
  • The number of features in the output layers varies with the number of unique incidences of features in the input layers.

eRAMS GIS_Union_Features Example


  • All attributes from input layers are included in the attribute table of the outputs layer.
  • The feature IDs of input layers are included in the attribute table of the output layer.
  • The attributes from input layers are represented as separate fields in the output layer attribute table, even when the field names are the same.
  • The values of the attributes from input fields are obtained from the corresponding input layers and are left blank for output features that are not encompassed in the input layer.

eRAMS GIS_Union_Attribute Table Example



API Notes

Code Sample