GIS Lecture 9 Spatial Analysis. Outline. Proximity Buffers Spatial Joins on Buffers Visual Basic Scripts Apportionment. Proximity Buffers. Proximity. Buffers Created Points Lines Polygons. Points. Buffer created by assigning a buffer distance around points.
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Buffer created by assigning a buffer distance around points
- Polygon buffer created ¼ and ½ mile around schools
Polygon buffer 20’ around lights in a parking lot
Buffer created by assigning a buffer distance around lines
Access-to-Work Study (Pittsburgh Foundation)
- Polygon buffer created around PAT Bus Routes
- Shows 15 minute ride times
Another buffer shows 30 minute ride times
- Polygon buffer created ¼ mile around selected streets
Buffer created by assigning a buffer distance around polygons
Advanced calculations for finding area, perimeter, and length of features
Result is the area of each polygon feature
Export attributes as table
Add as XY Data…
Population by voting district
Apportioning (makes approximate splits) of each tract’s data to two or more car beats.
Better to use census block centroid data
Zoomed view of 2 car beats and one tract
Apportionment assumes that the fraction of under educated persons 25 or older is the same as that for the general population aged 25 or older:
From the block centroids, create a new summary table counting the number of persons Age22+ for each census tract
Check Apportionment Weights
Values should all