Landscape Suitability
Readings:
Steinitz, Carl, Paul Parker,
and Laurie Jordan, 1986. Hand-drawn overlays: their history and prospective
uses. Landscape Architecture 66(5) 444-455.
Hopkins, Lewis D., 1987.
Methods
for Generating Land Suitability Maps: A Comparative Evaluation.
AIP
Journal, October 1987. 386-400.
Relating information from different sources
Population
If you want to lobby the city for a new health clinic in your neighborhood,
or if you are thinking of opening a grocery store, you'd better know how
many people live in the surrounding area in order to assess the suitability
of the proposed location for your intended use. If the people are
thinly spread and younger, the city will have better places to put its
clinic and the grocery store may go belly-up with not enough customers.
Population density is the number of people living in a certain defined
area -- in the US this is usually people per square mile. The primary
information source to find out about people and population in the United
States is the US Census. It is a count of all people living in the United
States and takes place every ten years. It contains information like family
size, education, income etc. The following chart shows the number of people
per square mile in and around East St. Louis -- the Emerson Park neighborhood,
Belleville, St. Clair county. The map shows that density reported
as a map to show how it varies from place-to-place.
East St. Louis has some areas with many people and some areas with relatively
few people. Most of the neighborhoods have a high population density while
areas that are parks, industry, commercial, or rail yards have no population
density. St. Clair County has two major urban centers. They are East
St. Louis and Belleville. These areas have a higher population density
than the rest of the county. They appear as the darkest areas on the map.
Other smaller dark areas are other towns in the county. Cities and
towns have a higher population density than the surrounding farming areas
because people live closer together. East St. Louis has from 2,467
to 38,000 people per square mile living together while the surrounding
farming areas have from zero to 658 people per square mile. (Other
data on ESL)
Although Census data can show a lot of information about a neighborhood,
it cannot show how population data relate to oher kinds of data such as
biophysical or land-use data. To do that would need access to information
about those features.
Land condition - Pollution
City councils keep accurate maps of streets showing how wide they are and
if they are in good shape. These maps are used for emergency services and
for planning bus routes etc. The county keeps accurate information on property
ownerships so they know who to tax, and where they need to provide new
schools and parks. The state collects information as different as the locations
of historic homes and schools and the location of toxic wastes.
Imagine you want to find a home to rent, in a quiet neighborhood and
far from any known locations for toxic materials. The following shows information
about CERCLA sites where the U.S. Environmental Protection Agency (EPA)
has identified locations of toxic spills etc. in East St. Louis, in both
text and map form.
CERCLIS
Site Information
Site Name: PFIZER INC Address: 2001 LYNCH EAST ST LOUIS, IL 62202
EPA ID: ILD006317119 EPA Region: 05 County: 163 ST CLAIR NPL
Status: Not on the NPL Federal Facility Flag: Not a Federal Facility Incident
Category:
URL: http://www.epa.gov/oerrpage/superfund/sites/cursites/c3il/s0500237.htm
Compatible and incompatible land uses
The city and county keep records of land uses to help them decide where
to build new services. Often cities keep a Zoning Map that shows where
you can build certain types of property -- it keeps homes and industry
separated. You can also get maps that show where it floods regularly, where
the streams run, how high the ground is, and what kinds of soils are around.
If you are building a home and want to keep your basement dry you'll need
that kind of information! But it is important even if you are a long-term
resident. The following map shows the different land uses in East St. Louis.
While most of the land use in the city is homes (viable housing) residents
need to keep track of zoning plans to make sure they don't change and bring
a highway or factory close to their homes. On this map you can see the
commercial strip that runs along State Street across the entire city and
the pockets of industrial sites scattered throughout.
Selecting suitable sites
The key issue here is the need to relate information from different sources
in order to give guidance to future decisions - to assess the suitability
of the land for new purposes.
The key attribute of any of the information described which enables
it to be related is a spatial reference.
-
As a rule, such information enters into the decision-making process most
usually as a map.
-
To make the comparison of such maps convenient the various data sources
are made available to the same scale and same map projection.
-
Taking that one step further, if maps were available on transparent media
it would be possible to overlay the maps and directly see the spatial relationships.
The overlay mapping technique that results, popularized by landscape architects
and planners such as Ian McHarg and furthered by others such as Steinitz
and Hopkins, is one of the most important planning and management tools
available to land planning. In its computerized format, the Geographic
Information System, overlay mapping provides a powerful tool for management
and manipulation of spatial data.
Example
(from United
States Geological Survey Introduction to GIS)
If you could relate information about the rainfall of your State to
aerial photographs of your county, you might be able to tell which wetlands
dry up at certain times of the year. A GIS, which can use information
from many different sources, in many different forms can help with such
analyses. The primary requirement for the source data is that the locations
for the variables are known. Location may be annotated by x,y, and z coordinates
of longitude, latitude, and elevation, or by such systems as ZIP codes
or highway mile markers. Any variable that can be located spatially can
be fed into a GIS. Several computer data bases that can be directly entered
into a GIS are being produced by Federal agencies and private firms. Different
kinds of data in map form can be entered into a GIS.
A GIS can also convert existing digital information, which may not yet
be in map form, into forms it can recognize and use. For example, digital
satellite images can be analyzed to produce a map like layer of digital
information about vegetative covers. Likewise, census or hydrologic
tabular data can be converted to map-like form, serving as layers of thematic
information in a GIS.
The U.S. Geological survey (USGS), in a cooperative project with the
Connecticut Department of Natural Resources, digitized more than 40 map
layers for the areas covered by the USGS Broad Brook and Ellington 7.5-minute
topographic quadrangle maps.
This information can be combined and manipulated in a GIS to address planning
and natural resource issues. GIS information was used to locate a potential
site for a new water well within half a mile of the Somers Water Company
service area.
To prepare the analysis, digital maps of the water service areas were stored
in the GIS. Using the buffer function in the GIS, a half-mile zone was
drawn around the water company service area.
This buffer zone was the "window" used to view and combine the various
map coverages relevant to the well site selection. The land use and
land cover map for the two areas shows that the area is partly developed.
A GIS was used to select undeveloped areas from the land use and land cover
map as the first step in finding well sites. The developed areas were eliminated
from further consideration.
The quality of water in Connecticut streams is closely monitored. Some
of the streams in the study area were known to be unusable as drinking
water sources. To avoid pulling water from these streams into the wells,
100-meter buffer zones were created around the unsuitable streams using
the GIS, and the zones were plotted on the map.
The map showing the buffered zone was combined with the land use and land
cover map to eliminate areas around unsuitable streams from the analysis.
The areas in blue have the characteristics desired for a water well site.
Point sources of pollution are recorded by the Connecticut Department
of Natural Resources. These records consist of a geographic location and
a text description of the pollutant.
To avoid these toxic areas, a buffer zone of 500 meters was established
around each point.
This information was combined with the previous two map layers to produce
a new map of areas suitable for well sites.
The map of surficial geology shows the earth materials that lie above bedrock.
Since the area under consideration in Connecticut is covered by glacial
deposits, the surface consists largely of sand and gravel, with some glacial
till and fine-grained sediments. Of these materials, sand and gravel are
the most likely to store water that could be tapped with wells. Areas underlain
by sand and gravel were selected from the surficial geology map
and combined with the results of the previous selections to produce a new
overlay map consisting of sites in undeveloped areas underlain by sand
and gravel that are more than 500 meters from point sources of pollution
and more than 100 meters from unsuitable streams.
A map shows that the thickness of saturated sediments was created by using
the GIS to subtract the bedrock elevation from the surface elevation.
For this analysis, areas having more than 40 feet of saturated sediments
were selected and combined with the previous overlays. The resulting
site selection map shows areas that are undeveloped, are situated outside
the buffered pollution areas, and are underlain by 40 feet or more of water-saturated
sand and gravel.
Because of map resolution and the limits of precision in digitizing, the
very small polygons (areas) may not have all of the characteristics analyzed,
so another GIS function was used to screen out areas smaller than 10 acres.
The final six sites are displayed with the road and stream network and
selected place names for use in the field.
The process illustrated by this site selection analysis has been used for
a number of common applications, including transportation planning and
waste disposal site location. The technique is particularly useful when
several physical factors must be considered and integrated over a large
area.
Practical 7 (Continued)
Readings for next Monday:
American Forests - Trees Fight Sprawl
US
News & World Report article***
A Pixel Worth
a Thousand Words: Satellite images reveal startling tree loss in American
cities.
***get
the Acrobat
Reader
Trees
Fight Sprawl -- http://www.amfor.org/garden/trees_cities_sprawl/tcs_subhome.html
Sprawl
Campaign -- http://www.amfor.org/garden/trees_cities_sprawl/sprawl/sprawl_subhome.html
Modified: 22 October 1999, Brian Orland
