Spatial Expression

Spatial Expression adds a spatial expression-based schema column to an overlay.

Click View > Table to open the table window.

Now click Add and select Spatial Expression to display the Spatial expression type dialog:

You can also access this command from the Overlays dialog > Schema tab > Column drop-down:

Option Description

Count

Counts the number of Items on another Overlay whose origin is within a Polygon on this Overlay.

Sum

Adds up the values of an expression on Items on another Overlay whose origin is within a Polygon on this Overlay.

Average

Averages the values of an expression on Items on another Overlay whose origin is within a Polygon on this Overlay.

Overlap

Calculates the area of overlap between a Polygon on this Overlay and Polygons on another Overlay.

Contained

Retrieves a property value from an Item on another Overlay that is within a Polygon on this Overlay.

Container

Retrieves a property value from a Polygon on another Overlay that contains the origin of an Item on this Overlay

Examples of spatial expressions

The Map Window below shows an SWD with Polygon Items on each of three overlays:

For examples of each spatial expression options, click here.