GIS Lecture: Spatial Joins

Spatial Joins

Spatial join example You have census block group centroid points with housing fuel data You want to know housing fuel use for whole neighborhoods But there are no attributes in common Spatial join is needed

Spatial joins Points to polygons Spatially joins points (block centroids) within polygons (neighborhoods) Joins using “shape” (not an attribute field)

Spatial joins Right-click the polygon layer (neighborhoods)

Join result New polygon feature

Join result Count – how many points are in each neighborhood Sums – adds up the field values within each neighborhood

Count result Number of points in each polygon

Sum result One neighborhood example Central business district 4 block groups Housing units with electricity fuel from block group centroids field [H040004] (80 + 299 + 128 + 292 ) Sum = 799

Choropleth map result (sum)

Spatial Joins