Count points in polygon
Q: How can I count the number of points which fall into polygons?
A: Carry over an attribute from the polygons to the points, then count the number of equal attributes by SQL grouping: Example: How many archaeological sites does each parcel owner have?
# Spearfish area # (Note: DBF driver unsupported, please use SQLite, MySQL or PostgreSQL) g.copy vect=archsites,myarchsites v.db.addcol myarchsites col="owner varchar(25)"
We now transfer the owner names to the archaeological sites (points):
v.what.vect myarchsites qvect=fields column=owner qcolumn=label # verification: v.db.select myarchsites d.mon x0 d.vect -c fields d.vect myarchsites icon=basic/diamond size=10 # test run echo "SELECT *,count(owner) FROM myarchsites GROUP BY owner" | db.select # upload to polygons map g.copy vect=fields,myfields v.db.addcol myfields col="numpoints integer" v.db.update myfields column=numpoints value="(SELECT count(owner) FROM myarchsites WHERE myarchsites.owner=myfields.label GROUP BY owner);" # verification: v.db.select myfields
The resulting polygon table contains the number of points falling into each polygon.