NCGIA Core Curriculum in Geographic Information Science
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Unit 186 - The Polygon Overlay Operation

(Unit 34 from the original Core Curriculum, 1990)

compiled for the original Core Curriculum with assistance from
Denis White, Environmental Protection Agency, Corvallis, OR

This unit is part of the NCGIA Core Curriculum in Geographic Information Science. These materials may be used for study, research, and education, but please credit the the project, NCGIA Core Curriculum in GIScience. All commercial rights reserved.  Copyright 1997 by NCGIA.

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Unit 186 - The Polygon Overlay Operation

(Unit 34 from the original Core Curriculum, 1990)

NOTE: This unit was written for the original version of the NCGIA Core Curriculum in GIS, published by the NCGIA in 1990.  It has not been edited for inclusion in this new version, but its content is timeless and still as useful as it was originally.

1. Introduction

1.1. Traditions of polygon overlay use

1.1.1. Landscape planning

1.1.2. Set theoretic

1.1.3. Area interpolation

2. General concepts of polygon overlay operations

2.1. Operations requiring polygon overlay

2.1.1. Windowing

2.1.2. Buffering


2.1.3. Planar Enforcement

3. Overlay algorithms

3.1. Example of overlay operation




3.2. A more complex overlay example

4.  Computational complexity

5. Intersection problems

5.1. Adjacent lines

5.2. Sliver polygons

5.2.1. Removing slivers during overlay

5.2.2.  Removing slivers after overlay

6. 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.

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

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

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

7. References


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First posted on WWW: October 7, 1997.  Last revised: October 7, 1997.

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