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Wildlife Ecology
Updated 26 August 2009
Chapter 21 (old book) – Geographic Information Systems (GIS)
Chapter 15 (new book) – Application of Spatial Technologies in Wildlife Biology
A GIS consists of software, hardware, and personnel for performing spatial analysis.
GIS has become very important in natural resource management.
What is a GIS?
According to Aronoff (1989:39), a GIS is defined as:
“A computer-based system that provides the following four sets of capabilities to
handle georeferenced data:
1)
2)
3)
4)
input
data management (data storage and retrieval)
manipulation and analysis
output
Other definitions out there, but the above is the basis.
Spatial data have 2 components:
1)
a geographic reference
2)
an attribute
Locations can be recorded in a number of ways, possibilities include:
1)
UTM – Universal Transverse Mercator coordinates
2)
State plane coordinates
3)
Latitude and longitude
4)
Other (arbitrary) coordinate systems
The 5 basic questions that a GIS can be used to answer were described by Walker and
Miller (1990):
1)
2)
3)
4)
5)
What exists at a particular site?
Where are certain conditions met?
What changes have occurred over time and where have these changes
occurred
What are the social, economic, or environmental impacts of a particular
change in the use of land?
What will happen if the existing land use for a particular site is altered to
another type of use?
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Location can be described in many ways and can be defined as a:
1)
Point, line, area (polygon)
2)
By place name (street address, city, county, or wildlife management area),
post or ZIP code, geographic coordinates (i.e., UTM, state plane, latitude
and longitude)
GIS Data Structures
3 general features of the data within a GIS must be maintained:
1)
information on the position of the feature being stored
2)
topological information on the spatial relationships of the features
(topology is the way in which geographic features are connected and
provides a mechanism to identify the positional relationships among
features)
3)
attributes of the feature
spatial data types are referenced to a location by a standard system of coordinates, such as
UTM – see page 542, especially read Box 1 about UTM.
Spatial data can be represented as either rasters or vectors
In raster format, a grid is used to represent the study area. The location of the
features in the study area is depicted by the values in the cells overlaying the features.
See Fig. 2, page 543 (old book), which compares raster and vector format.
Vector data represent geographic features by coordinates of points, lines, and
polygons.
Raster Data
Raster data are stored in the computer as a matrix – see Fig 3, page 543 (old book).
The cells are referenced by lines and elements. In the simplest form, each line is a
computer record. Each record will contain the values for all elements in the line.
Any cell not containing a feature would have the value of “0.”
In the simplest raster system, the value stored for each cell is the attribute component of
the geographic data. See Fig. 4, page 544 (old book)
Because the raster system is strictly a 2-dimentional matrix, various types of geographical
data are stored as different layers or overlays in the GIS – see Fig. 5, page 544 (old
book). (For example, one layer might be ground cover, 1 layer wetlands, 1 layer roads)
User of raster system must decide on cell size (i.e., degree of resolution) – bigger cells
allow you to store more information, but they allow less precision—have to make the
decision of what is best for the objectives of your study.
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Vector Data
Vector data provide for high precision in representing the locations of features.
A point is represented by a simple pair of coordinates.
A line is represented by an ordered list of pairs of coordinates.
The area is represented as a polygon with ordered pairs of coordinates that close the
polygon (the first and last pair being the same).
As mentioned before, UTM, state plane, or latitude and longitude coordinates can be
used.
Early systems used simple techniques to store X and Y coordinates for polygons –
however, in this case, the coordinates for the common boundary between 2 areas were
stored twice- wasted storage space and, more importantly, provided no information as to
adjacency or connectivity of geographic features (topology).
Most vector systems now use topological models for representing locations of areas.
In topological models – polygon is defined by series of arcs – see Fig. 6, page 545 (old
book).
Arcs begin and end at nodes, which occur wherever 2 or more arcs meet.
Each arc is defined by a series of coordinates, starting with the coordinates for the
beginning node and ending with the coordinates for the ending node.
Topological relationships are stored in 3 tables:
1) polygon table – describes the arcs that bound
each polygon
2)
node topology table – describes the arcs that end
at each of the nodes
2)
arc topology table – describes which end points
(nodes) occur on each arc and which polygons
are to the left and the right of each arc.
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These 3 tables provide the tools required to efficiently determine the positional
relationships of one feature to other features.
A coordinate table defining the coordinates for each arc is also used in topological
models.
In addition to these topological databases, the attributes for the features are stored in an
attribute database.
Raster versus Vector Systems
Early GISs were either raster or vector systems.
Today, most GISs handle both kinds of data, but they are usually designed primarily for 1
type of data.
See Table 1, page 546, for advantages and disadvantages for each system (old book)
Data for the GIS
Most of the cost of a GIS is in acquiring and maintaining data (our book says about
60-90% of the cost).
As data are gathered, accuracy and reliability of all data layers should be documented.
Documentation should include:
1)
2)
3)
4)
5)
date the information was collected
positional accuracy
classification accuracy
completeness
procedures used to collect and encode the data
The following gives some methods of acquiring GIS data.
1)
Manual Keyboard Data Entry – especially used for attribute data but
can be used to enter other data as well.
2)
Manual Digitizing – here, a map or aerial photograph is placed on a
digitizing table and a pointing device is used to record coordinates of
feathers to be extracted from the map – time consuming and error
prone.
3)
Scan Digitizing – flatbed scanners, video scanners, drum scanners,
etc.
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4)
Remote Sensing Techniques – defined as any technique by which we
gather data about an object without directly touching the object –
data for GIS applications are often obtained by satellite or aircraft.
a)
LANDSAT – is the US land remote sensing satellite systemfirst developed by NASA and LANDSAT 1 was launched on 23
July 1972; read about history.
b)
SPOT – (Systeme Pour l’Observation de la Terre) – first SPOT
satellite launched by France in 1986.
c)
Coastal Zone Color Scanner (CZCS) – launched on the
Nimbus-7 Satellite by the US government in 1978 and operated
until June 1986. It measures ocean color and temperature.
d)
AVHRR Sensor – in 1979 the NOAA-6 satellite and all
subsequent satellites in the NOAA series carried the
“Advanced High Resolution Radiometer (AVHRR) sensor. It
measures reflected radiation in the red and near infrared
wavelengths and emitted thermal radiation in 3 spectral bands.
e)
GOES Satellite (Geostationary Operational Environmental
Satellites) – they orbit the earth at an altitude of 36,000 km in
the same direction as the earth’s rotation – therefore, the
maintain a stationary position relative to the earth.
f)
MOS-1 – read
g)
JERS-1 – read
h)
ERS-1 – read
i)
RADARSAT – read
j)
Aircraft Sensors – read
k)
Videography – read
Existing Databases
1)
Land Use and Land Cover (LULC) and Associated Maps - from
USGS. They provide data on 5 layers:
a. Land use and cover
b. Political units
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c. Hydrologic units
d. Census county subdivisions
e. Federal land ownership
2)
Digital Line Graphs (DLG) – digital representation of the planimetric
information (line map data)
3)
Digital Elevation Data – read
4)
National Wetlands Inventory (NWI) - read
5)
Digital Soils Data - read
6)
DIME Files (Dual Independent Map Encoding) – street networks,
street addresses, political boundaries, major hydrographic feathers of
about 350 major cites and suburbs in US – some limitations in
application as a digital map base.
7)
TIGER Files (Topologically Integrated Geographic Encoding and
Referencing) – census-type data
Read over the rest of the chapter.