Vector Analysis 2

Intro to GIS - Week 10

Week 10's lab was on Vector Analysis using modeling tools in ArcGIS such as buffer and overlay, creating a scrips in ArcPy to run the buffer tool, and spatial queries.  To perform these analysis we started with layers for roads, lakes & rivers, and conservation areas.  Our goal was to create a map showing possible camping sites in De Soto National Forest in Mississippi, that would be within 300 meters of a road, and either within 150 meters of a lake or 500 meters of a river, but not within any conservation areas.  This was the resulting map:

To create this we first needed to create buffer zones of our parameters for roads and waters.  We did this first for roads by using the Proximity Analysis Tool Buffer.  With the Buffer tool we created a buffer of 300 meters on all the roads.  Next, since rivers and lakes were on the same layer and we wanted different distances for rivers than we did for lakes we first created a new field in the attribute table then selected by Attributes to assign values for the variable buffer distance. Once that was done we were able to run the Buffer tool using this new field.

We also created several buffers using ArcPy mostly to see how it was done.  ArcPy makes more sense to use for multiple processes because you can run them all at once so it saves a lot of time.  

Once our buffering was done we needed a way to combine the information for the two datasets.  For this we used the Overlay Analysis Tool called Union.  Again, to prepare the data to be combined, we had to first prepare the attribute tables to provide the information required for the process.  We did this by adding fields to both the buffered water and the buffered roads layers assigning a value of 1 to the fields for inside the buffer zones of water and roads.  After that we ran the Union Tool.  The output of this process was a layer with the combined data.  Once all this information was altogether in one file we then were able to run a query to select by attribute only those records that fell within the buffer zones for both water and roads and export those features to a new feature class.

We now had a layer that contained only those buffer zones that fit our criteria for roads and water.  Next we added the conservation area to the mix by using the Erase overlay tool to remove from our selection set any buffered areas that fell within the boundaries of the conservation areas.  This provided us with our ultimate goal of selecting possible campsites that were within 300 meters of a road and either within 150 meters of a lake or 500 meters of a river, but not within a conservation area.  It seems a little convoluted, but it works.