Module 8 - Application in GIS - Least-Cost Path and Corridor Analysis

In the last regular lab for Application in GIS this term, we worked on least cost paths and corridors.  This is somewhat similar to suitability analysis, in that we can assign weights and values to various criteria, then combine them to obtain a final best result.

Instead of suitability, we refer to "cost" in this type of study.  Cost can be time, or money, or anything else we must expend to get from a source to a destination.

In this type of analysis, a cost surface is computed, and from that a cost-distance surface.  The latter calculates the cells of a raster that are easiest to travel across, based on the criteria, from a source to a destination.  We can then produce an ideal path across the surface that will incur the minimum cost of travel.

A corridor can also be found from one place to another.  Instead of a single, one-cell-wide path, the corridor is a zone of lesser cost.  We can specify a  threshold to define the corridor, saying that only costs below a certain value are desirable.  The map here shows a movement corridor for black bears between two areas of National Forest in Arizona.  The criteria for finding the corridor were land cover type, elevation, and distance from roads.  The green area on the map shows the most optimal area through which the bears can travel from either direction, between the two tracts of National Forest.

Module 7 - Applications in GIS - Spatial Accessibility Modeling

This week in Application in GIS, we worked with spatial accessibility modeling.  This is the analysis of how well people are able to get to facilities that they need in their communities.  We use the ArcMap Network Analysis extension for this type of study.  The network dataset consists of streets, junctions, and many attributes associated with them, such as speed limits, stops, one-ways streets and other restrictions and impediments to flow of traffic.  By inserting the locations of facilities that people need to access, along with locations or zones in which people travel from, we can plot the fastest or most direct routes.
In this particular assignment, we examined the impact of the closure of a community college on the population of Travis County, Texas.  The above map shows polygons created in Network Analysis for the travel times from each census block group to the closest college campus of the Austin Community College system.   In the right-hand map, the travel times are examined for the six remaining campuses when the northern-most campus (Cypress Creek, represented by the red dot on the left-hand map) is closed.  Further analysis of the census block group data in Network Analyst revealed that more than 4000  people between the ages of 18 and 29 (most potentially college-aged) live closest to the Cypress Creek campus, and would have to travel further to an alternate campus if their nearest campus were closed.  In the event that Cypress Creek Campus were closed, most of these displaced potential students would be next-closest to the Northridge Campus. and a few would be closest to the Pinnacle Campus.  The average increase in travel time for those displaced potential students to their new college campuses is about 9 minutes.