GEOGRAPHIC
INFORMATION
SYSTEMS
(GIS)
-------
GIS
OVERVIEW
Geographic Information Systems provide data en-
try, storage, manipulation, analysis, and display
capabilities for geographic, environmental, cultural,
statistical, and political data in a common spatial
framework.
The data analyzed are a collection of spatial informa-
tion (represented by points, lines, and polygons) and
their associated text attributes (characteristics of the
features which the points, lines, and areas repre-
sent).
Spatial
Features
The attribute data associated with these spatial data
may include ownership information, chemical char-
acteristics, or economic activities. Sources of data for
GISs include maps, aerial photographs, satellite
images, censuses, field measurements, and meteoro-
logical records.
-------
Graphics Workstation
Plotter
Digitizer
GISs are fully integrated systems that analyze and
map spatial data, and provide statistical and com-
puter graphic products.
GIS technology bridges the disciplines of computer
science (including image processing and pattern
recognition), information management, cartogra-
phy, and environmental management. The GIS is
distinguished from other systems by its ability to
perform spatial analysis.
Typical
GIS
Configuration
-------
GIS
SPATIAL DATA FEATURES
Map
Overlay
The geographic location of each data item (or "attrib-
ute") is a key identifier used to describe and organize
data in a GIS. Maintaining the integrity of this spatial
descriptor as part of the data base record permits
normal data base management system operations
and adds the capability to manipulate and analyze
data geographically. The concept of data analysis in
relation to geographic position is commonly en-
countered in map reading.
A major GIS analytical function is to assign colors or
patterns to multiple map themes and overlay them
to reveal spatial relationships.
LAND COVER
SOIL TYPES
TRANSPORTATION
HYDROLOGY
TOPOGRAPHY
Geographic data can be represented using either of
two formats - - vector/polygon or raster/grid data
structures.
-------
Vector/polygon data structures describe unique
lines or forms of geographic features. A lake, for
example, can be described by the coordinates which
comprise the circumference of the outer lake bound-
ary and can be captured and stored in the GIS as a
tracing of these features.
COORDINATE POINTS
PLOT OF VECTOR MAP
VECTOR FORMAT
• POINTS
• LINES
• POLYGONS
GRID-CELL FORMAT
• CELLS
• PIXELS
a&• neap GIB
COOED GRID CELLS
PLOT OF GRID-CELL MAP
Data
Formats
Raster/grid data refers to attribute values and spa-
tial references tied to specific x, y intersections or
grids in space (e.g., latitude/longitude). Fine grid
spacing allows high resolution and good definition
of spatial characteristics.
EPA's standard GIS tool, ARC/INFO, has the capa-
bility to handle both data structures.
-------
GIS
FUNCTIONS
Data
Entry
II
The data entered into a GIS often include spatial data
from maps, remote sensors (aerial photography and
satellite imagery), and environmental monitoring.
GISs require entry of two distinct types of data:
geographic references and attributes.
Geographic reference data are the coordinates
which describe the location of spatial information.
This type of data entry often occurs via a process
known as digitization. A special peripheral device
— a digitizer — is used to convert a drawing or map
into a digital format. Another method of capturing
map data uses a special device called a scanner. GIS
also allows data input via key-entry at a terminal,
reading a magnetic tape, or downloading from a
separate computer system.
-------
The characteristics which distinguish a GIS from
other data base management systems and manual
map overlay procedures is the way a GIS stores the
spatial data and makes it available for user access
and analysis.
Derived maps and data sets may become part of the
GIS data base in a feedback process that permits
future retrieval and display without rerunning the
analysis procedure. These map and data layers can
be superimposed during analysis to produce vari-
ous map products with the GIS information display
functions. This data generation process requires
special spatial analysis and tabulation capabilities
provided through the data base management sys-
tem.
SPATIAL
DATA
Ambient Water Quality
> Water Quality
• Sample Protocal
• Analytic Method
ATTRIBUTE
INFORMATION
SPATIAL
DATA
BASE
NON-
SPATIAL
DATA
BASE
Data
Base .
Management
-------
GIS
FUNCTIONS (continued)
Data
Manipulation
Boolean
Model Overlay
DISTORTION
REMOVAL
PROJECTION
CHANGE
COORDINATE
ROTATION
AND
TRANSLATION
--?
The GIS data base management system provides the
ability to query, manipulate, and extract both geo-
graphic reference and attribute data.
One of the major functions of a GIS is the analysis of
multiple levels of data in a selected geographic area.
With a GIS, standard statistical manipulations of
attribute data are possible, as are boolean queries of
attribute data files, generation of mean and standard
deviation for numerical data ranges, and classifica-
tion of data into mappable units.
AND, OR, NOT, and GROUP
AN! i
RESULT
-------
POINT
BUFFERS
BOUNDARY AND
CONTOUR
GENERATION
' 4,
T v ¥
LINE
BUFFERS
OPTIMUM
CORRIDOR
ANALYSIS
Data
Analysis
Other GIS data manipulation and analysis capabili-
ties include querying unique spatial distributions of
data and asking questions about data to display
unique spatial arrangements which meet a specific
criterion.
Information display includes the representation of
base data and of the results of data manipulation and
analysis. Outputs fall into several categories: maps,
charts, graphs, surface models, and tabular listings.
A comprehensive geographic information system
supports various computer mapping and graphics
peripherals. Geographic/spatial analysis of data
usually precedes data display, although initial dis-
play of raw data is useful for developing a final
output product.
HARDCOPY MAPS
GRAPHIC DISPLAYS
TABULAR LISTINGS
Display
Capabilities
-------
APPLICATION OF
GIS TO EPA PROGRAMS
Corvallis
Agency programs use numerous types of environ-
mental data obtained from a variety of sources. This
information may include an assortment of historic
scientific reports available in manual files, data
extracted from current EPA systems or other state
and Federal data bases, or the results of other moni-
toring activities.
GISs can provide the linkages necessary for effective
environmental decision-making, program priori-
ties, and associated implementation plans by inte-
grating and mapping environmental data. Decision-
makers can then set priorities and develop pollution
controls based on this spatial information.
The benefits realized from use of a GIS in Agency
programs are linked to spatial data integration (e.g.,
surface water quality data combined with land use
and NPDES data) and the capability to display and
analyze these data on maps at a common scale.
The Direct Delay Response Project (DDRP) examines the possible
long term response of surface water to continued acid deposition.
The GIS at the Environmental Research Laboratory-Corvallis (ERL-
C) plays a vital role in a variety of analytical procedures and predic-
tive models with the DDRP. The National Lakes Survey used a
stratified random sample to infer both chemical characteristics of
lakes and the number of lakes at risk to acid deposition. The GIS at
ERL-C provides database management mapping capabilities and the
ability to extrapolate chemical values from these sampled lakes to
non-sampled lakes. Mapping for the National Stream Survey in-
cludes the production of maps showing site locations, circle maps
depicting chemical parameters, and residual plots of regression
analysis using chemical and physical parameters for sample sites.
-------
The Region IV GIS and its subsystems form an integral part of the
Region's Results Analysis and Management System (RAMS), and
provide for geographically referenced information analysis and
display as well as cross-media data integration.
The most useful product to date is a process for predicting the
probable size of a target population, through the ground water route,
in the vicinity of a Superfund site. The end result of this processing,
a combination of both geographic and traditional methods, will be a
listing of Superfund sites sorted on approximate HRS ranking to
assist the program in directing its efforts to those sites with the largest
likelihood of actually becoming NFL sites.
The Environmental Monitoring Systems Laboratory in Las Vegas,
Nevada (EMSL-LV) has embarked on a series of pilot studies based
on the use of GIS technology to investigate spatial data system ap-
proaches. The focus of the pilot studies is hazardous waste sites
which fall under RCRA or CERCLA guidance. The employed meth-
ods involve the integration of remote sensing, geophysical and field
data into a spatial data base to be used for site remedial investigations
and future management.
Primary GIS analyses for the San Gabriel Basin CERCLA site in
Southern California consists of determining the populations at risk
from contaminated wells and tracking the movement of pollution
through the aquifer. Water purveyor districts are overlaid with con-
taminated wells and digital census data to provide maps of popula-
tions at risk from contaminants.
A major objective of this task is to develop the ability to pinpoint
contaminant sources. The laboratory is using ARC/INFO interfaced
with a model to identify eight discrete potential contaminant sources.
The Program Systems Division of the Office of Information Re-
sources Management in EPA Headquarters, Washington D.C., is
responsible for management of GIS technology on a national scale.
For further information, contact Mr. Joseph Sierra PM-218B, Na-
tional GIS Coordinator, 401 M Street SW, Washington D.C. 20460.
Telephone FTS 382-7868/202 382-7868. EMail: EPA 3783,
Region IV
Las Vegas
OIRM
------- |