UNIT 34 - THE POLYGON OVERLAY OPERATION

UNIT 34 - THE POLYGON OVERLAY OPERATION

UNIT 34 - THE POLYGON OVERLAY OPERATION

A. INTRODUCTION

Traditions of polygon overlay use

B. GENERAL CONCEPTS OF POLYGON OVERLAY OPERATIONS

Operations requiring polygon overlay

C. OVERLAY ALGORITHMS

Objective

Given Procedure

D. COMPUTATIONAL COMPLEXITY

E. INTERSECTION PROBLEMS

1. Adjacent lines

2. Sliver polygons

Removing slivers during overlay

Removing slivers after overlay

REFERENCES

McHarg, I.L., 1969. Design with Nature, Doubleday, New York

Goodchild, M.F., and N. S. Lam, 1980. "Areal Interpolation," Geoprocessing 1:297-312.

DISCUSSION AND EXAM QUESTIONS

1. McHarg described the overlay technique well before the advent of GIS and polygon overlay. Discuss the advantages and possible disadvantages of a computer implementation of the technique.

2. Write out and illustrate the 16 Boolean combinations of two polygons A and B.

3. Review and discuss the alternative forms of areal interpolation described by Goodchild and Lam, 1980.

4. Discuss the relative advantages of raster and vector approaches to polygon overlay. Identify the application areas likely to adopt each method given their advantages.


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