Week 11 -GIS - Vector Analysis II

A map created using buffering and overlay tools in ArcGIS

This week in Intro to GIS, we learned about using various tools for vector analysis.  The goal of the exercise was to identify the zones in which campsites might be built in the area of interest in the De Soto National Forest, Mississippi.  The criteria are that the campsites must lie within certain distances of both roads and water bodies, and must not overlap the conservation areas, in which plants and animals are protected.

To identify the zones that are a certain distance from the roads and water bodies, we use the Buffering tool in ArcMap.  Buffering involves drawing a line a specific distance from a point, line or another polygon. The area inside the line forms a new polygonal feature which is the buffer. In the case of this map, the buffers surround lakes, rivers and roads at a distance of 150, 500 and 300 meters respectively.  We want the campsites to lie within the buffers:  they should be close to both roads and water bodies.

Use of the union tool combines all of the features of two or more layers, while the intersect tool combines only those features that are common to both layers: that is, their intersection.
In this case, we used the intersect tool to identify the areas on the map that are within the buffers of both the roads and water layers: in other words, the areas that are within minimum specified distances of both roads and water features, as given by the buffer operations described above.

Once this intersection layer was isolated, we performed one more operation with the Erase tool:  it excludes the features (or area covered) of a third layer, namely the Conservation Area layer, from the layer created by the intersection of the water and road buffer.  We do not want the campsites to lie within these areas (shown in light green above).

The final result gives us possible sites for campsites, and shown in pink above.