ESM 263 Geographic Information Systems

Bolstad Lab 9 cheat sheet

Bolstad’s Lab 9 is a good intro to buffering and overlay, but it’s a bit too complicated for its own good (so to speak.) Here’s a simpler way to do it.

Buffering

To create the variable distance buffers around the lakes, instead of messing with the attribute table, do this:

1. Select Vector→Geoprocessing Tools→Buffer

2. Under Distance, click on the Data defined override button (next to meters) and select Edit…

3. Paste this text into the Expression box:

   CASE
   WHEN SIZE_CLS = 1 THEN 50
   WHEN SIZE_CLS = 2 THEN 150
   WHEN SIZE_CLS = 3 THEN 500
   END
   

4. Click OK, then Run

Overlay

Again, no need to mess with the attribute tables, or with the geometries. Just run the following tools:

1. Difference (variable lakes buffer − lakes)
2. Intersection (difference ∩ roads buffer)
3. Difference (intersection − public)