2

I have two polygon layers. One represents parcels, the other is a hazard zone. How do I return only parcels where more than 30% of the parcel area overlaps the hazard zone? For example a parcel with an area of 100,000 square feet with 35,000 square feet inside the hazard zone should be returned as it's 35% overlap. On the other hand, a parcel of 100,000 square feet with 5,000 square feet inside (overlapping) the hazard area should not be returned as it's only 5% overlap.

I tried st_intersects but, although I get the parcels that overlap the hazard are, I need to take into account the percentage of overlap. How do I compare areas of overlap versus parcel area?

select p.id from parcels p, hazard h where st_intersects(p.geom, h.geom)
2

You can calculate the interesection of both layers and compare it to the area of the original geometry.

SELECT p.id 
FROM parcels p
JOIN hazard h ON ST_Intersects(p.geom, h.geom)
WHERE ST_Area(ST_Intersection(p.geom, h.geom)) / ST_Area(p.geom) > 0.35;

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.