Information That Supplements Lecture 2
What is GIS?
From the NCGIA Core Curriculum - Compiled with assistance from David Cowen, University of South Carolina
A.
INTRODUCTION
B.
CONTRIBUTING DISCIPLINES AND TECHNOLOGIES
C.
MAJOR AREAS OF PRACTICAL APPLICATION
D.
GIS AS A SET OF INTERRELATED SUBSYSTEMS
REFERENCES
There are several ways you might consider beginning your introductory
course in GIS. This unit attempts to put GIS into context. However, it
lacks visual images and anecdotes that only the instructor can provide.
There are several ways you may want to supplement this unit. Consider beginning
this unit by showing an introductory video on GIS. A promotional video
from a vendor demonstrating applications of GIS and types of output would
be suitable. Or take the students into the lab and let them play with a
packaged GIS demo.
UNIT 1 - WHAT IS GIS?
From the NCGIA Core Curriculum - Compiled with assistance from David Cowen, University of South Carolina
A.
INTRODUCTION
Objectives
of this unit
- to examine various definitions of GIS - what factors uniquely differentiate
it from other forms of automatic geographical data handling?
- to determine origins of the field - how does GIS relate to other fields
such as statistical analysis, remote sensing, computer cartography?
- to give a brief overview of the relevant application areas
What
is a GIS?
- a particular form of Information System applied to geographical data
- a System is a group of connected entities and activities which interact
for a common purpose
- a car is a system in which all the components operate together to provide
transportation
- an Information System is a set of processes, executed on raw data,
to produce information which will be useful in decision-making
- a chain of steps leads from observation and collection of data through
analysis
- an information system must have a full range of functions to achieve
its purpose, including observation, measurement, description, explanation,
forecasting, decision-making
- a Geographic Information System uses geographically referenced data
as well as non-spatial data and includes operations which support spatial
analysis
- in GIS, the common purpose is decision-making, for managing use of
land, resources, transportation, retailing, oceans or any spatially distributed
entities
- the connection between the elements of the system is geography, e.g.
location, proximity, spatial distribution
- in this context GIS can be seen as a system of hardware, software and
procedures designed to support the capture,
management, manipulation, analysis, modeling and display of spatially-referenced
data for solving complex planning and management problems
- although many other computer programs can use spatial data (e.g. AutoCAD
and statistics packages), GISs include the additional ability to perform
spatial operations
Alternative
names
- alternative names which people have used over the years illustrate
the range of applications and emphasis
Why
is GIS important?
- "GIS technology is to geographical analysis what the microscope,
the telescope, and computers have been to other sciences.... (It) could
therefore be the catalyst needed to dissolve the regional-systematic and
human- physical dichotomies that have long plagued geography" and
other disciplines which use spatial information.1
- GIS integrates spatial and other kinds of information within a single
system - it offers a consistent framework for analyzing geographical data
- by putting maps and other kinds of spatial information into digital
form, GIS allows us to manipulate and display geographical knowledge in
new and exciting ways
- GIS makes connections between activities based on geographic proximity
- looking at data geographically can often suggest new insights, explanations
- these connections are often unrecognized without GIS, but can be vital
to understanding and managing activities and resources
- e.g. we can link toxic waste records with school locations through
geographic proximity
- GIS allows access to administrative records - property ownership, tax
files, utility cables and pipes - via their geographical positions
Why
is GIS so hot?
- high level of interest in new developments in computing
____________________ 1Abler, R.F., 1988. "Awards, rewards and excellence:
keeping geography alive and well," Professional Geographer, 40:135-40.
- GIS gives a "high tech" feel to geographic information
- maps are fascinating and so are maps in computers
- there is increasing interest in geography and geographic education
- GIS is an important tool in understanding and managing the environment
Market
value of GIS
- Fortune Magazine, April 24, 1989 published a major, general-interest
article on the significance of GIS to business:
- GIS is described as a geographical equivalent of a spreadsheet, i.e.
allows answers to "what if" questions with spatial dimensions
- an example of the value of GIS given in the article is the Potlatch
Corporation, Idaho
- controls 600,000 ac of timberland in Idaho - 4,900 separate timber
stands
- old method of inventory using hand-drawn maps meant that inventory
was "hopelessly out of date"
- $180,000/year now being spent on GIS-based inventory "a bargain"
- GIS "gives Potlatch up-to-the-minute information on the status
of timber.... A forest manager sitting at a terminal can check land ownership
changes in a few minutes by zooming in on a map"
- $650,000 on hardware and software produces more than 27% annual return
on investment
- GIS market
- Dataquest projected a market of $288 million in 1988, $590 million
in 1992 for GIS, growing at 35% per year
- ESRI of Redlands, CA, developers of ARC/INFO, had 350 employees and
sales of $40 million in 1988 and a reported 42% increase in sales in 1989
- Intergraph had 1988 sales of $800 million in a more diverse but GIS-dominated
market
- the 1989 edition of GIS Sourcebook listed over 60 different "GIS"
programs (though not all of these have complete GIS functionality) and
over 100 GIS consultants (US)
B.
CONTRIBUTING DISCIPLINES AND TECHNOLOGIES
- GIS is a convergence of technological fields and traditional disciplines
- GIS has been called an "enabling technology" because of the
potential it offers for the wide variety of disciplines which must deal
with spatial data
- each related field provides some of the techniques which make up GIS
- many of these related fields emphasize data collection - GIS brings
them together by emphasizing integration, modeling and analysis
- as the integrating field, GIS often claims to be the science of spatial
information
Geography
- broadly concerned with understanding the world and man's place in it
- long tradition in spatial analysis
- provides techniques for conducting spatial analysis and a spatial perspective
on research
Cartography
Remote
Sensing
- images from space and the air are major source of geographical data
- remote sensing includes techniques for data acquisition and processing
anywhere on the globe at low cost, consistent update potential
- many image analysis systems contain sophisticated analytical functions
- interpreted data from a remote sensing system can be merged with other
data layers in a GIS
Photogrammetry
- using aerial photographs and techniques for making accurate measurements
from them, photogrammetry is the source of most data on topography (ground
surface elevations) used for input to GIS
Surveying
- provides high quality data on positions of land boundaries, buildings,
etc.
Geodesy
- source of high accuracy positional control for GIS
Statistics
- many models built using GIS are statistical in nature, many statistical
techniques used for analysis
- statistics is important in understanding issues of error and uncertainty
in GIS data
Operations
Research
- many applications of GIS require use of optimizing techniques for decision-making
Computer
Science
- computer-aided design (CAD) provides software, techniques for data
input, display and visualization, representation, particularly in 3 dimensions
- advances in computer graphics provide hardware, software for handling
and displaying graphic objects, techniques of visualization
- database management systems (DBMS) contribute methods for representing
data in digital form, procedures for system design and handling large volumes
of data, particularly access and update
- artificial intelligence (AI) uses the computer to make choices based
on available data in a way that is seen to emulate human intelligence and
decision-making - computer can act as an "expert" in such functions
as designing maps, generalizing map features
- although GIS has yet to take full advantage of AI, AI already provides
methods and techniques for system design
Mathematics
- several branches of mathematics, especially geometry and graph theory,
are used in GIS system design and analysis of spatial data
Civil
Engineering
- GIS has many applications in transportation, urban engineering
C.
MAJOR AREAS OF PRACTICAL APPLICATION
Street
network-based
- address matching - finding locations given street addresses
- vehicle routing and scheduling
- location analysis, site selection
- development of evacuation plans
Natural
resource-based
- management of wild and scenic rivers, recreation resources, floodplains,
wetlands, agricultural lands, aquifers, forests, wildlife
- Environmental impact analysis (EIA)
- viewshed analysis
- hazardous or toxic facility siting
- groundwater modeling and contamination tracking
- wildlife habitat analysis, migration routes planning
Land
parcel-based
- zoning, subdivision plan review
- land acquisition
- environmental impact statements
- water quality management
- maintenance of ownership
Facilities
management
- locating underground pipes, cables
- balancing loads in electrical networks
- planning facility maintenance
- tracking energy use
D.
GIS AS A SET OF INTERRELATED SUBSYSTEMS
Data
Processing Subsystem
- data acquisition - from maps, images or field surveys
- data input - data must be input from source material to the digital
database
- data storage - how often is it used, how should it be updated, is it
confidential?
Data
Analysis Subsystem
- retrieval and analysis - may be simple responses to queries, or complex
statistical analyses of large sets of data
- information output - how to display the results? as maps or tables?
Or will the information be fed into some other digital system?
Information
Use Subsystem
- users may be researchers, planners, managers
- interaction needed between GIS group and users to plan analytical procedures
and data structures
Management
Subsystem
REFERENCES
Bylinsky, Gene, 1989. "Managing with Electronic Maps," Fortune
April 24, 237-254. Good review of the state of GIS in mid-1989 from a commercial
perspective.
Cowen, D.J., 1988. "GIS versus CAD versus DBMS: what are the differences?"
Photogrammetric Engineering and Remote Sensing 54:1551-5. Excellent review
of the differences in these three traditions.
Dueker, K.J., 1987. "Geographic information systems and computer-aided
mapping," Journal, American Planning Association 53:383-90. Compares
CAD, computer cartography and GIS, conceptually and also at some technical
depth.
Fisher, P.F., and R. Lindenberg, 1989. "On distinctions among Cartography,
Remote Sensing, and Geographic Information Systems," Photogrammetric
Engineering and Remote Sensing 55(10):1431-1434. Reviews definitions of
each of the three and shows how the disciplines are interrelated.
Marble, D.F. et al., 1983. "Geographic information systems and
remote sensing," Manual of Remote Sensing. ASPRS/ACSM, Falls Church,
VA, 1:923-58. Reviews the various dimensions of the relationship between
the two fields.
Parent, P. and R. Church, 1987. "Evolution of Geographical Information
Systems as Decision Making Tools," Proceedings, GIS '87, pp. 63-71,
ASPRS/ACSM, Falls Church, VA. Good review of the history of GIS and its
formative influences.
Rhind, D., 1989. "Why GIS?," Arc News, Summer 1989, Vol 11(3).
MAPS AND MAP ANALYSIS
From the NCGIA Core Curriculum - Compiled with assistance from David Rhind, Birkbeck College, University
of London
Helpful Web Sites:
Cartographic Communication (Foote and Crum/Geographer's Craft) -- Elements
of effective cartographic design. -
Cartography/Maps (U of Western Ontario)
-
Fundamental of Cartography (NAIS) -- Illustrated and described: Map
projections; tables showing properties of projections.
-
Map Projection Overview (Dana/Geographer's Craft)
-
Thematic and Base Map images of Canada (NAIS) -- Thematic maps (e.g.
ethnic diversity, satellite image); Base maps (e.g. Canada base map series,
world).
-
What Does Analytical Cartography have to do with GIS? (Chrisman/U of
Washington) -- GIS definitions; schools of thought about maps and mapping.
A. INTRODUCTION
B. WHAT IS A MAP?
C. WHAT ARE MAPS
USED FOR?
D. THE USE OF
MAPS FOR INVENTORY AND ANALYSIS
E. AUTOMATED AND
COMPUTER-ASSISTED CARTOGRAPHY
F. GIS COMPARED
TO MAPS
REFERENCES
This unit explores the map analysis roots of GIS. We have placed it
early in the sequence as we feel the issues discussed here determine to
a large extent how GIS users presently view the role of GIS and it should
help to put later lectures into perspective. Illustrate this unit with
several examples of different kinds of maps from your map collection.
UNIT 2 - MAPS AND MAP ANALYSIS
From the NCGIA Core Curriculum - Compiled with assistance from David Rhind, Birkbeck College, University
of London
A. INTRODUCTION
- maps are the main source of data for GIS
- the traditions of cartography are fundamentally important to GIS
- GIS has roots in the analysis of information on maps, and overcomes
many of the limitations of manual analysis
- this unit is about cartography and its relationship to GIS - how does
GIS differ from cartography, particularly automated cartography, which
uses computers to make maps?
B. WHAT IS A MAP?
Definition
- according to the International Cartographic Association, a map is:
- a representation, normally to scale and on a flat medium, of a selection
of material or abstract features on, or in relation to, the surface of
the Earth
Maps show
more than the Earth's surface
- the term "map" is often used in mathematics to convey the
notion of transferring information from one form to another, just as cartographers
transfer information from the surface of the Earth to a sheet of paper
- the term "map" is used loosely to refer to any visual display
of information, particularly if it is abstract, generalized or schematic
Cartographic
abstraction
- production of a map requires:
- selection of the few features in the real world to include
- classification of selected features into groups (i.e. bridges, churches,
railways)
- simplification of jagged lines like coastlines
- exaggeration of features to be included that are to small to show at
the scale of the map
- symbolization to represent the different classes of features chosen
Types of
maps
- in practice we normally think of two types of map:
- topographic map - a reference tool, showing the outlines of selected
natural and man-made features of the Earth
- often acts as a frame for other information
- "Topography" refers to the shape of the surface, represented
by contours and/or shading, but topographic maps also show roads and other
prominent features
- thematic map - a tool to communicate geographical concepts such as
the distribution of population densities, climate, movement of goods, land
use etc.
Thematic
maps in GIS
- several types of thematic map are important in GIS:
- a choropleth map uses reporting zones such as counties or census tracts
to show data such as average incomes, percent female, or rates of mortality
- the boundaries of the zones are established independently of the data,
and may be used to report many different sets of data
- an area class map shows zones of constant attributes, such as vegetation,
soil type, or forest species
- the boundaries are different for each map as they are determined by
the variation of the attribute being mapped, e.g. breaks of soil type may
occur independently of breaks of vegetation
- an isopleth map shows an imaginary surface by means of lines joining
points of equal value, "isolines" (e.g. contours on a topographic
map)
- used for phenomena which vary smoothly across the map, such as temperature,
pressure, rainfall or population density
Line maps
versus photo maps
- an important distinction for GIS is between a line map and a photo
map
- a line map shows features by conventional symbols or by boundaries
- a photo map is derived from a photographic image taken from the air
- features are interpreted by the eye as it views the map
- certain features may be identified by overprinting labels
- photomaps are relatively cheap to make but are rarely completely free
of distortions
Characteristics
of maps
- maps are often stylized, generalized or abstracted, requiring careful
interpretation
- usually out of date
- show only a static situation - one slice in time
- often highly elegant/artistic
- easy to use to answer certain types of questions:
- how do I get there from here?
- what is at this point?
- difficult or time-consuming to answer other types:
- what is the area of this lake?
- what places can I see from this TV tower?
- what does that thematic map show at the point I'm interested in on
this topographic map?
The concept
of scale
- the scale of a map is the ratio between distances on the map and corresponding
distances in the real world
- if a map has a scale of 1:50,000, then 1 cm on the map equals 50,000
cm or 0.5 km on the Earth's surface
- the use of the terms "small scale" and "large scale"
is often confused, so it is important to be consistent
- a large scale map shows great detail, small features
- representative fraction is large, e.g. 1/10,000
- a small scale map shows only large features
- representative fraction is small, e.g. 1/250,000
- the scale controls not only how features are shown, but what features
are shown
- a 1:2,500 map will show individual houses and lamp posts while a 1:100,000
will not
- different scales are used in different countries
- in the US, 1:100,000 is the largest scale at which complete coverage
of the continental states exists, but there is limited coverage at 1:62,500
and 1:24,000
- in the UK, there is complete coverage at much larger scales (1:1,250
to 1:10,000)
Map projections
- the Earth's surface is curved but as it must be shown on a flat sheet,
some distortion is inevitable
- distortion is least for when the map only shows small areas, and greatest
when a map attempts to show the entire surface of the Earth
- a projection is a method by which the curved surface of the earth is
represented on a flat surface
- it involves the use of mathematical transformations between the location
of places on the earth and their projected locations on the plane
- numerous projections have been invented, and arguments continue about
which is best for which purposes
- projections can be identified by the distortions which they avoid -
in general a projection can belong to only one of these classes:
- equal area projections preserve the area of features by assigning them
an area on the map which is proportional to their area on the earth - these
are useful for applications which require measuring area, and are popular
in GIS
- conformal projections preserve the shape of small features, and show
directions (bearings) correctly - they are useful for navigation
- equidistant projections preserve distances to places from one or two
points
C. WHAT ARE MAPS
USED FOR?
- traditionally, maps are used as aids to navigation, as reference documents,
and as wall decorations
- maps have four roles today:
Data display
- maps provide useful ways of displaying information in a meaningful
way
- in practice, the cost of making and printing a map is high, so its
contents are often a compromise between different needs
Data stores
- as a means of storing data, maps can be very efficient, high density
stores
- a typical 1:50,000 map might have 1,000 place names on it
- the distances between all possible pairs of these 1,000 places would
run to (1,000 x 999 / 2) or 499,500 numbers if stored in a table instead
of scaled off the map when needed
- the information printed on the typical 1:50,000 topographic map sheet
in the UK requires 25 million bytes of storage when it is converted to
digital form, equivalent to one standard computer tape, or 10 full-length
novels
- the information on all British topographic maps would require 150 gigabytes
(150x109 bytes)
Spatial indexes
- a map can show the boundaries of areas (e.g. land use zones, soil or
rock types) and identify each area with a label
- a separate manual with corresponding entries may provide greater detail
about each area
Data analysis
tool
- maps are used in analysis to:
- make or test hypotheses, such as the identification of cancer clusters
- examine the relationship between two distributions using simple transparent
overlays
D. THE USE OF MAPS
FOR INVENTORY AND ANALYSIS
- the following examples demonstrate how maps have been used for sophisticated
applications in inventory and analysis, and point out some limitations
Measuring
land use change
- example, two major land use surveys were carried out in the UK, in
the late 1930s by Sir Dudley Stamp and in the 1960s by Professor Alice
Coleman
- the results were published as maps
- in order to compare changes in land use between 1930s and 1960s, the
area of each land use type was measured using a hand planimeter and counting
overlaid dots
- despite interest in measuring the amount of change of land use through
time, particularly from agricultural to
urban, few results were produced using this method because the traditional
techniques are slow and tedious, and because of the difficulty of overlaying
or working from very different map sources
Landscape
architecture
- Ian McHarg pioneered the use of transparent map overlays for planning
locations of highways, transmission corridors and other facilities in environmentally
sensitive areas (McHarg, 1969)
- despite the popularity of this technique and numerous applications,
this method remains cumbersome and imprecise
E. AUTOMATED AND
COMPUTER-ASSISTED CARTOGRAPHY
Changeover
to computer mapping
- personalities were critically important in the 1960s and early 1970s
- individual interests determined the direction and focus of research and
development in computer cartography (see Rhind, 1988)
- impetus for change began in two communities:
1. scientists wishing to make maps quickly to see the results of modeling,
or to display data from large archives already in digital form, e.g. census
tables
- quality was not a major concern
- SYMAP was the first significant package for this purpose, released
by the Harvard Lab in 1967
2. cartographers seeking to reduce the cost and time of map production
and editing
- hardware costs limited interest in this technology prior to 1980 to
the major mapping agencies
- the costs of computing have dropped dramatically, by an order of magnitude
every six years
- what costs $1 to compute in 1989 would have cost $10 in 1983 and $100,000
in 1959
- the development of the microcomputer and the launch of the IBM PC in
1983 have had enormous influence
- an early belief that the entire map-making process could be automated
diminished by 1975 because of difficulties of generalization and design
- has resurfaced in the context of Expert Systems where the computer
chooses the proper techniques based on characteristics of the data, scale,
map purpose, etc.
- today, far more maps are made by computer than by hand
- now few mapmakers are trained cartographers
- also, it is now clear that once created, digital data can serve purposes
other than map-making, so it has additional value
Advantages
of computer cartography
- lower cost for simple maps, faster production
- greater flexibility in output - easy scale or projection change - maps
can be tailored to user needs
- other uses for digital data
Disadvantages
of computer cartography
- relatively few full-scale systems have been shown to be truly cost-effective
in practice, despite early promise
- high capital cost, though this is now much reduced
- computer methods do not ensure production of maps of high quality
- there is a perceived loss of regard for the "cartographic tradition"
with the consequent production of "cartojunk"
GIS and Computer
Cartography
- computer cartography has a primary goal of producing maps
- systems have advanced tools for map layout, placement of labels, large
symbol and font libraries, interfaces for expensive, high quality output
devices
- however, it is not an analytical tool
- therefore, unlike data for GIS, cartographic data does not need to
be stored in ways which allow, for example, analysis of relationships between
different themes such as population density and housing prices or the routing
of flows along connecting highway or river segments
F. GIS COMPARED
TO MAPS
Data stores
- spatial data stored in digital format in a GIS allows for rapid access
for traditional as well as innovative purposes
- nature of maps creates difficulties when used as sources for digital
data
- most GIS take no account of differences between datasets derived from
maps at different scales
- idiosyncrasies (e.g. generalization procedures) in maps become "locked
in" to the data derived from them
- such errors often become apparent only during later processing of digital
data derived from them
- however, maps still remain an excellent way of compiling spatial information,
e.g. field survey
- maps can be designed to be easy to convert to digital form, e.g. by
the use of different colors which have distinct signatures when scanned
by electronic sensors
- as well maps can be produced by GISs as cheap, high density stores
of information for the end user
- however, consistent, accurate retrieval of data from maps is difficult
- only limited amounts of data can be shown due to constraints of the
paper medium
Data indexes
- this function can be performed much better by a good GIS due to the
ability to provide multiple and efficient cross-referencing and searching
Data analysis
tools
- GIS is a powerful tool for map analysis
- traditional impediments to the accurate and rapid measurement of area
or to map overlay no longer exist
- many new techniques in spatial analysis are becoming available
Data display
tools
- electronic display offers significant advantages over the paper map
- ability to browse across an area without interruption by map sheet
boundaries
- ability to zoom and change scale freely
- potential for the animation of time dependent data
- display in "3 dimensions" (perspective views), with "real-time"
rotation of viewing angle
- potential for continuous scales of intensity and the use of color and
shading independent of the constraints of the printing process, ability
to change colors as required for interpretation
- one of a kind, special purpose products are possible and inexpensive
REFERENCES
Dobson, J.E., 1983. "Automated geography," Professional Geographer
35:135-43. Compares the potential of digital and conventional map use.
See also the set of discussions published in the next issue.
Goodchild, M.F., 1988. "Stepping over the line: technological constraints
and the new cartography," American Cartographer 15:311-9. Argues that
cartography's traditions are derived from its reliance on pen and paper,
and looks at how these constraints are removed by automation.
McHarg, I.L., 1969. Design With Nature, Doubleday, New York. The definitive
work on the use of map analysis in landscape architecture.
Rhind, D.W., 1988. "Personality as a factor in the development
of a discipline: the example of computer- assisted cartography," American
Cartographer 15:277-90. Examines the history of the digital revolution
in cartography and the effect of key personalities.
Tobler, W.R., 1959. "Automation and cartography," Geographical
Review 49:526-34. An early perspective and prophesy.
Tomlinson, R.F., 1988. "The impact of the transition from analogue
to digital cartographic representation," American Cartographer 15:249-62.
An overview from a pioneer of GIS.
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