Class Notes: Computational Problems and Research in GIS II

Spring 1998 - Mon 4:05-6:00pm, Thu 5:10-6:00pm CSE/E440

Instructors: G.X. Ritter and M.S. Schmalz

Project 2 Assignment

• Goal. The purpose of this project is to provide basic hands-on experience with GIS sensitivity analysis, as well as provide the opportunity to help you build a library of advanced GIS computational capabilities.

• Sources. We will be using the material on GIS sensitivity analysis presented in class, which is summarized in Section 3 of this set of Web pages.

• Features. The program will implement GIS sensitivity measures m₁ through m₅ as discussed in class, together with a polygon area computation routine.

• Procedure. Implement the following steps:

  Step 1. Build a utility to intersect polygons in n maps given polygon boundary coordinates.

  • Hints: Make your own source data files (maps) consisting of polygon vertices and a ranked attribute label (e.g., soil density or urban population density). You must choose the ranking scheme.

  • For example, given an MxN-pixel array X, create n Boolean source maps a₁,a₂, ..., a_n F^X with lines that represent polygon borders. Then, add the images to yield an integer-valued image b on an MxN-pixel array X. Wherever b(x) > 1, there exists a polygon boundary intersection, which might be a new polygon vertex not found in any of the polygons contained in the source maps.

  • When computing area, first locate all the polygon vertices, then traverse the boundary segments linking the vertices, marking the segments you traverse in a given direction. Recall that this method was discussed in detail when we presented methods of polygon area computation in the Fall semester.

  Step 2. Construct one or more procedures to compute the area of each polygon in the source maps and intersection map. You may use the trapezoidal rule, which we discussed in detail last semester.

  Step 3. For each of the sensitivity measures given in Section 3, build one subroutine or function per each measure (m₁ through m₅). You will have to construct an additional procedure to perform attribute ranking. If you use an attribute such as soil density, this is a simple matter of sorting the numerical values of the attribute in ascending or descending order.

  Step 4. Construct a main program that calls the sensitivity measures to perform both area-weighted and unweighted sensitivity analysis, per the methods discussed in class.

  Step 5. Design, but do not necessarily construct, a procedure that perturbs the source map attribute rankings, as we discussed in class. We will consider this process in greater detail in mid-April, so you don't have to build a program now.

• Programming Hints. You will find the project easier if you observe the following suggestions:
  1. Use a standard programming language, such as C or Matlab.

  2. Share your code for the intersection routine, and try to make the procedure as efficient as possible.

  3. Test your program thoroughly on test maps that you make so that you can control the program's input.