Discussion 2: Overlay Combinations
Map Combination Applications
Purpose
The overlay operation is central to many applications of GIS,
and one of the original motivations in the creation of the software
technology. Applications in site suitability, for example, require
integration of multiple sources of geographic information. An
overlay uses a geometric process to associate all the attributes
at each location, then uses a rule to combine these attributes.
This case study will focus on the rules used in some actual GIS
applications.
Procedure
This case study will have a core resource:
Steven Carver: How
to dispose of Nuclear Waste in Britain, an internet decision
tool....
This site provides a way to explore the combination of two kinds
of overlay combination (constraints and factors). Explore this
site and its documentation.
You will then find a second application of overlay and
describe:
- What your second application was trying to do, and why they
used overlay; compare this to the core example
- How each source map was measured and represented (and what
attribute manipulations were done, if any); compare this to the
core reading
- Figure out how the attribute combination rule fits into the
taxonomy in Table 5-1 in the text; compare this to the core reading
- Give your opinion about the suitability of these steps for
the original purpose of both studies.
Issues to consider
Your preparation might consider the role of scale and resolution
(in attribute as well as spatial measurements).
Did the authors of the study deal with the quality of the
data sources (issues like positional accuracy, attribute accuracy,
logical consistency and completeness)?
- Is the method chosen deliberately, or is it imposed upon
the application by some external force?
Web-based papers using overlay (Select your second application
from these):
Nature
Park location in Farfax County Virgina
Locating Prisons
in Oregon (their gif links direct: screening
results, results)
Marina
Suitability (Coastal Services Center) not a paper, read the
metadata...
Change
detection project in Iran;
Real
estate development in South Carolina;
Suitability
for manure disposal in Indiana (no graphics, read between
the lines...);
Review of objectives:
- Each application exhibits these components:
- A particular purpose (articulated)
- Multiple sources of geographic information
- Use of some Overlay operation (technique to combine attributes)
- Examine the method of combination used, compared to
the core reading
- Relation to measurement framework and representation
- Strengths and weaknesses of choices made
- Produce a 2-3 page essay covering these points.
- Discuss in the class session the different examples discovered
- similarities and differences
Some starting points for possible web sites (and retired papers):
Index from Here: | Main
Index | Schedule of Lectures
| Schedule of Labs | How
to reach us
Version of 22 October 2003
