What Is a Geometric Intersection?
The intersection operation finds the area shared by two polygons. Given polygons A and B, the result is the region where both polygons overlap. If the polygons do not overlap, the result is empty.
How to Use the Intersection Tool
Provide two GeoJSON polygon inputs. The tool computes the overlapping area and returns it as a new GeoJSON geometry. The result is displayed on the map alongside the original inputs so you can verify the overlap region.
Common Use Cases
- Finding where two administrative boundaries overlap
- Determining the shared area between a buffer zone and a land parcel
- Calculating the overlap between flood zones and building footprints
- Identifying regions that satisfy two geographic criteria simultaneously
Related operations: union (total area of both polygons), difference (area in A but not in B), clip (trim features to a boundary).
Try It
Find the overlap between a Midtown rectangle and a Central Park rectangle. The two polygons share a strip where they overlap vertically:
GeoJSON{
"type": "Feature",
"properties": { "name": "Midtown" },
"geometry": {
"type": "Polygon",
"coordinates": [[[-73.99, 40.75], [-73.97, 40.75], [-73.97, 40.77], [-73.99, 40.77], [-73.99, 40.75]]]
}
}GeoJSON{
"type": "Feature",
"properties": { "name": "Central Park South" },
"geometry": {
"type": "Polygon",
"coordinates": [[[-73.985, 40.76], [-73.975, 40.76], [-73.975, 40.79], [-73.985, 40.79], [-73.985, 40.76]]]
}
}The result is a smaller rectangle covering only the overlap zone — from longitude -73.985 to -73.975, latitude 40.76 to 40.77. On the map this appears as a narrow strip where both input rectangles coincide, roughly around Columbus Circle.
How It Works
The intersection tool uses Turf.js (@turf/intersect), which computes the boolean intersection of two polygon geometries via the JSTS topology library. The algorithm identifies all edge crossings between the two polygons, then traces the path that lies inside both polygons simultaneously. If no overlap exists, the function returns null. For more on polygon operations, consult the GeoJSON specification guide.