Class STOverlayLayers

Extends STTransformVector

Spatially adds (union), subtracts, insertects, or finds the symetric difference
between the features in one layer from the features in another layer.

The features in both layers can be filtered based on selection.

Attributes can also be specified to be matched in each layer to have features
operated on by the matching features in the other layer.

Regardless, the operation is that for each layer in the first input layer:
- The features in the second layer are combined and then used to operate
on the feature in the first layer.
- The features in the second layer are either all combined or they can be filtered
by the ones that are selected or by matching attribute values in the first layer.

If an attribute column is provided in either layer, then each feature is operated
against each matching feature.

No Attributes specified: The second input layer is combined into a single geometry
that is used to operate on each feature in the first layer

Attribute columns specified in each layer: The layers features are operated on
by the matching features from the second input layer.

@author Jim Graham
Copyright, SchoonerTurtles LLP, 2009

Enumerated Types