Geospatial · Combine and measure
Spatial Intersection
Overlays two layers. Keep only where they overlap, or cut one out of the other, such as land parcels minus flood zones.
Also known as: Overlay, erase
How it works
Name the geometry column on each side (Left, Right) and the Operation. Intersection outputs one row per overlapping pair with both sides' attributes, and the overlap becomes the only geometry, in the Output column (named after the operation by default) in place of both source geometries. Difference outputs one row per left feature with every overlapping right shape subtracted at once; right attributes are dropped, a feature nothing overlaps passes through untouched, and a feature the right layer covers completely is dropped. Auto-reproject right side (on by default) transforms the right geometry onto the left's coordinate system when they differ.
Inputs and outputs
Inputs
left— Tableright— Table
Outputs
data— Table
Settings
The Attributes panel of Spatial Intersection, as in the app: the controls work, but nothing runs — there is no data behind it.
The same settings, as the Assistant writes them
{
leftGeom: string
rightGeom: string
operation: "intersection"|"difference"
outputColumn: string
}intersection joins intersecting pairs and the overlap ST_Intersection(left, right) becomes the sole geometry, keeping both sides' attributes; difference erases the right layer out of the left — one row per LEFT feature with every overlapping right geometry subtracted at once, right attributes dropped, fully covered features dropped. outputColumn defaults to the operation name and replaces the source geometries — feed it Spatial Measure for area/percent
Example
Land parcels minus flood zones: left is the parcels, right is the flood zones, operation Difference, output column dry_area. Then Spatial Measure on dry_area gives the usable area per parcel.