Supporting Resources

for Lecture 09: Overlay Basics

Index of Resources:

Site and Situation

In the economic geography of Edward Ullman (and others of the 1950s), site meant the local conditions, while situation referred to the surroundings. In this view, the pixel was not the model of site, a city could be a site.

Site Suitability

Original McHarg work Design with Nature

Recent Applications of Overlay for Suitability (MANY, links lost...)

Many regulations imply the use of Overlay Logic

Simple exclusionary logic built into regulation, eg. NEPA, WA Ecology,[such as Hazardous Waste Management, and the regulations for Medium Waste Facilities, see page 28 for the actual criteria...] WA Growth Management; (in specific the critical area designations WAC 365-190-080 - link failed)

"Classification is the first step in implementing RCW 36.70A.050. It means defining categories to which natural resource lands and critical areas will be assigned. Critical area ordinance for Spokane County

Critical areas include the following areas and ecosystems: 
(a) Wetlands; 
(b) Areas with a critical recharging effect on aquifers used for potable water; 
(c) Fish and wildlife habitat conservation areas; 
(d) Frequently flooded areas; 
(e) Geologically hazardous areas." (WAC 365-190-030-3)


Site suitability for Low Level Radioactive Waste in Pennsylvania;

Direct Analysis by Enumerating the Combinations

If two maps that are meant to be the same classes are overlaid, analysis can proceed immediately.

Change Detection

Error Analysis

Two replicates of the same classification after overlay produce a map of disagreements. Examples:

Gap Analysis:

Comparison of habitat range and protected areas: the general strategy: ; Washington examples.

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Version of 17 October 2003