GIS Lecture Spatial Joins GIS Tutorial Third Edition

GIS Lecture: Spatial Joins GIS Tutorial, Third Edition GIS 1

Spatial Joins GIS Tutorial, Third Edition GIS 2

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 GIS Tutorial, Third Edition GIS 3

Spatial joins Points to polygons • Spatially joins points (block centroids) within polygons (neighborhoods) • Joins using “shape” (not an attribute field) GIS Tutorial, Third Edition GIS 4

Spatial joins Right-click the polygon layer (neighborhoods) GIS Tutorial, Third Edition GIS 5

Join result New polygon feature GIS Tutorial, Third Edition GIS 6

Join result • Count – how many points are in each neighborhood • Sums – adds up the field values within each neighborhood GIS Tutorial, Third Edition GIS 7

Count result Number of points in each polygon GIS Tutorial, Third Edition GIS 8

Sum result One neighborhood example • Central business district - 4 block groups - Housing units with electricity fuel from block group centroids field [H 040004] (80 + 299 + 128 + 292 ) - Sum = 799 GIS Tutorial, Third Edition GIS 9

Choropleth map result (sum) GIS Tutorial, Third Edition GIS 10

Spatial Joins GIS Tutorial, Third Edition GIS 11