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Presented by William Huber, Ph.D.
Quantitative
Decisions, Merion, PA and
Penn State-Great Valley, Malvern, PA |
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What GIS is and is not. |
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Key GIS components and techniques. |
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How GIS works. |
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Examples of GIS analyses. |
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Examples of GIS applications. |
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Helping With Global Problems |
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The major challenges we face in the world
today--overpopulation, pollution, deforestation, natural disasters--have a
critical geographic dimension. |
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Helping With Local Problems |
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Whether investigating an industrial
facility or figuring out the best
route for an emergency vehicle, local problems also have a geographic
component. |
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A geographic information system (GIS) is a
computer-based tool for mapping and analyzing things that exist on and
events that happen on Earth: |
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It is a general purpose tool; that is, it can be
applied in many ways to many problems, including many not anticipated by
the GIS designers. |
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It must be able to select desired data from
among potentially very large stores of information |
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It must be able to pre-process those data into a
format suitable for mapping or analysis. |
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It must be able to post-process results into
graphics, tables, reports, and maps. |
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GIS technology integrates common database
operations such as query and statistical analysis with the unique visualization
and geographic analysis benefits offered by maps. |
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GIS readily converts data between different data
models (unlike most database and statistical software). |
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These abilities distinguish GIS from other information
systems and make it valuable to a wide range of public and private
enterprises for explaining events, predicting outcomes, and planning
strategies. |
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mapping |
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geographic data storage, retrieval, and
conversion |
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database management |
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statistical analysis |
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visualization |
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geographic analysis |
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GIS delivers useful map making and analytical
capabilities to groups and by long distance over the Internet. |
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Map making and geographic analysis are not new,
but a GIS performs these tasks better and faster than do the old manual
methods. |
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GIS is optimized to perform certain kinds of
data analyses involving distance, area, direction, and so on, better than
other computer software. |
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Aerial photography |
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Soils |
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Water |
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Digital elevation models (DEM, DTED) |
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Government agencies |
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U.S. states |
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General GIS information |
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Geodesy |
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Instructional materials and journals |
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Interactive mapping |
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Metadata and standards |
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Transportation GIS |
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Organizations |
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Software |
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Remote sensing |
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Cartography |
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(Before GIS technology, only a few people had
the skills necessary to use geographic information to help with decision
making and problem solving.) |
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Today, GIS is a multi-billion-dollar industry
employing hundreds of thousands of people worldwide. |
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GIS is taught in schools, colleges, and
universities throughout the world. |
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Professionals in many fields are increasingly
aware of the advantages of thinking and working geographically. |
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Internet users of GIS are rapidly growing in
numbers. |
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Business Support |
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Spatial information augments the management of
traditional business practices: customer management, marketing, logistical
planning, retail site selection, and so on. |
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Personal Productivity |
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A majority of software users indicate they would
like to “communicate with maps.” |
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GIS Professionals |
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These people acquire, create, edit, and
integrate spatial data, develop the systems used in business and modeling
applications, and, increasingly, develop Internet applications to enhance
the accessibility of geographic data to occasional or casual users. |
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A working GIS integrates these key components: |
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hardware |
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software |
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data |
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people |
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methods |
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Hardware is the computer on which a GIS
operates, including the resources available to the computer: |
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printers |
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plotters |
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digitizers |
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scanners |
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monitors |
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network |
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wide area communications |
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Today, GIS software runs on a wide range of
hardware types, from centralized computer servers to desktop computers used
in stand-alone or networked configurations. |
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GIS software provides the functions and tools
needed to |
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store |
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query |
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display |
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analyze |
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create |
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modify |
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data. |
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Key software components are |
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tools for the input, manipulation, reformatting,
and output of geographic data |
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a database management system (DBMS) |
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tools for geographic query, analysis, and
visualization |
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a graphical user interface (GUI) for easy access
to tools |
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tools to document data sources and quality (metadata) |
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Possibly the most important component of a GIS
is the data. Geographic data and
related tabular data can be collected in-house, found on the Internet for
free, or purchased from a commercial data provider. A GIS will integrate spatial data with
other data resources and can even use a DBMS, used by most organizations to
organize and maintain their data, to manage spatial data. (Many GISes are moving toward the use of
standard DBMSes, such as Oracle, for core database management functions.) |
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New data can also be entered into a GIS in many
different ways, including: |
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Digitizing from a digitizer |
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Heads up digitizing |
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GPS |
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Spatial “events” |
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Surveys, via COGO (computer geometry operations) |
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Scanned images |
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Acquisition from remote sensing instrumentation |
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GIS technology is of limited value without the people
who manage the system and develop plans for applying it to real world
problems. |
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GIS is a general purpose tool. What makes it work at all is the
“application domain” knowledge of the system designers and operators who
actually apply this tool. To use
GIS effectively in a navigation application requires specialized knowledge
of navigation principles, for example. |
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A successful GIS operates according to a
well-designed plan and business rules (or scientific rules), which are the
models and operating practices unique to each organization. |
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These models will determine database designs,
the formats in which geographical data are stored, and the specialized
software used for analysis. |
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A GIS stores information about the world as a
collection of thematic layers that can be linked together by geography.
This simple but powerful and versatile concept has proven invaluable for
solving many real-world problems from tracking delivery vehicles, to
recording details of planning applications, to modeling global atmospheric
circulation. |
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Object models |
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“Vector” data |
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Zero dimensions: |
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Points |
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Multipoints |
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One dimension: |
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Line segments |
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Polylines |
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Splines |
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Two dimensions: |
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Polygons |
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“Raster” data |
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Indicator grids |
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Categorical grids |
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Continuous field models |
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“Vector” data: |
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Irregularly spaced sample points |
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Contours |
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Polygons |
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Triangular [interpolation] net, or TIN |
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“Raster” data: |
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Regularly spaced sample points |
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Cell grid (numeric values) |
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Network models |
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Planar embedding of a one-dimensional graph
plus: |
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Point events |
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Segment events |
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Address models |
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Rule base for addressing a street network |
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General purpose GISes essentially perform five
processes or tasks. |
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Input |
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Manipulation |
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Management |
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Query and Analysis |
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Visualization |
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Before geographic data can be used in a GIS, the
data must be converted into a suitable digital format. The process of
converting data from paper maps into computer files is called digitizing. |
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Modern GIS technology has the capability to
automate this process fully for large projects using scanning technology;
smaller jobs may require some manual digitizing (using a digitizing table). |
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Today many types of geographic data already
exist in GIS-compatible formats. These data can be obtained from data
suppliers and loaded directly into a GIS. |
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Data can be obtained directly from commercial or
government sensors on satellites or aircraft. |
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GPS and sensor data can be combined to create
point or polyline data sets. |
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A myriad of external formats exist. Data loss in transformation from one
format to another must be assessed, documented, and minimized. |
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Conversion between certain formats, such as
between vector and raster representations, inherently creates a loss of
information. |
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Different formats support different levels of precision
and resolution. |
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It is likely that data types required for a
particular GIS project will need to be transformed or manipulated in some
way to make them compatible with your system. |
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For example, geographic information is available
at different scales (street centerline files might be available at a scale
of 1:100,000; census boundaries at 1:50,000, postal codes at 1:10,000, and
surveyed points at 1:500). Before this information can be integrated, it
must be referenced to the same datum, projected in a consistent manner, and
transformed to the same scale. This
could be a temporary transformation for display purposes or a permanent one
required for analysis. |
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GIS technology offers many tools for
manipulating spatial data and for weeding out unnecessary data. How and how well the software implements
these tools is a primary determinant of its ease of use and its cost. |
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Changing datums (for example, from NAD 27 to NAD
83) can be difficult or cumbersome. |
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Projections are usually implemented using power
series approximations that might be inadequate for high precision work. |
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Manipulating raster data sets usually requires
resampling and interpolation, which can introduce errors and cause a loss
of resolution. |
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Manipulation of linear features, including
polygon boundaries, often creates nonlinear objects that have to be
approximated with linear representations. |
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For small GIS projects it may be sufficient to
store geographic information as simple files. |
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Nowadays many GIS projects, even small ones, may
access data scattered throughout a network. Such data need special management. |
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It is best to use a database management system
(DBMS) to help store, organize, and manage data. (A DBMS is nothing more than computer software for managing a
database--an integrated collection of data.) |
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Managing changes is particularly difficult. Changes occur from resolving mismatches
among data sources and from updates caused by change over time. Present-day (early 2000) commercial
GISes have few or no tools to support this. |
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Data are stored conceptually as a collection of tables. |
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Common fields in different tables are used to
link them together. |
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This simple design has been widely used because
of its flexibility and wide deployment in many applications. |
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Many systems still physically separate the
geographic from the other (“attribute”) data, which can create
difficulties. |
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Most systems do not support managing information
about the data (the metadata). Such
support is crucial for overcoming the problems with data input and
manipulation. |
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There is no established methodology for managing
data change. |
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Mechanisms for assessing, storing, and
visualizing data accuracy are only in the research stage. |
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Once you have a functioning GIS containing your
geographic information, you can begin to ask simple questions such as |
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What proportion of prime agricultural land is
presently in use? |
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How far is it between a contaminant source and a
potentially exposed individual? |
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Where is land zoned for industrial use? |
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And analytical questions such as |
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Can the projected growth in infrastructure
support the predicted population increase within this area? |
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What is the dominant soil type for oak forest? |
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If I build a new highway here, how will traffic
be affected? |
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How will potential changes in weather and
climate affect the rate of snow melt? |
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No GIS can hope to support all the analytical
tools and models that are needed.
Every GIS needs mechanisms for incorporating user-written code and
interfacing with existing models. |
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Languages for analysis of specific kinds of
geographic data exist (such as for raster data) but are not standardized
the way SQL, for example, has been for database manipulation and query. |
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Many purely geographic analyses have many forms
of solution, often depending on how the data are represented. Lack of awareness of the trade-offs in
computing resources (execution time, RAM) causes many analyses never to be
done or to tie up computing workstations for weeks or months. |
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A modern GIS provides both simple
point-and-click query capabilities and sophisticated analysis tools to
provide timely information to managers and analysts alike. GIS technology really comes into its own
when used to analyze geographic data to look for patterns and trends, and
to undertake "what if" scenarios. Modern GISes have many powerful
analytical tools, but these are especially important: |
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Analysis of |
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Proximity |
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Adjacency |
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Containment |
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Overlay analysis |
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Evaluating connectedness (finding paths) |
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Typical questions: |
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How many low income households lie within two
miles of this proposed site? |
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What is the total number of soil samples within
50 feet of this pipeline? |
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What proportion of the alfalfa crop is within
500 m of the well? |
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How many people live within a twenty minute ride
from downtown? |
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To answer such questions, GIS technology often
uses a process called buffering to determine the proximity relationship
between features. |
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Typical questions: |
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Which developed regions lie on a fault line? |
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Which properties lie on or next to a flood
plain? |
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Which tracts have direct access to a
highway? To a lake? |
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Which species have habitats in contact with a
protected ecological region? |
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Performing every possible comparison is
time-consuming. A good GIS creates
internal data structures (“topology”) for finding answers rapidly. |
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Typical questions: |
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Which earthquake zones are located on land
masses? |
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Which crimes occurred within the Fifth District? |
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Which roads lie entirely within the local
jurisdiction? |
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Which habitats do not lie completely within
protected areas? |
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Clearly there are close relationships among
questions of proximity, adjacency, and containment. Often two or more of these techniques
are suitable for answering a question. |
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At its simplest, overlay is a visual operation,
but many analytical operations require one or more data layers to be joined
physically to show all distinct combinations of attributes. This overlay,
or spatial join, can integrate data on soils, slope, and vegetation, or
land ownership with tax assessment. |
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Typical questions: |
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Identify all portions of all properties with
greater than 15% slope. (Layers are
properties and slopes.) |
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Show regions where land use changed between 1990
and 2000. (Layers are land use 1990
and land use 2000.) |
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Identify the portions of a market service area
with population density greater than 50,000 people per square mile. (Layers are service areas and population
density.) |
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Modeling deposition of pollutants from air
emissions sources in the Netherlands |
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Managing water supply in a Morocco river valley |
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Studying corn production in central
Africa |
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Biodiversity assessment in Pennsylvania |
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Ecosystems analysis in Madagascar |
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Assessing the value of environmentally impaired
real estate in New Jersey |
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Tracking multi-phase contaminants in Silicon
Valley, California |
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Restoring natural habitat at Savannah River,
Georgia |
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The integration and analysis of highway crash
data in a GIS project |
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Intelligent crash location |
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Multimodal investment analysis |
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Traffic planning tools |
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Route selection and evaluation |
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Intelligent routing and logistics |
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Consumer information |
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Retail store site selection |
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Streamlining business mergers |
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Customer market analysis |
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Demographic analysis |
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Vehicle tracking |
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Emergency management |
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E-911 monitoring and dispatch |
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Delivery tracking |
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Wildlife tracking |
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Precision agriculture |
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Military asset management |
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GIS is rapidly becoming a key technology to
support decision making at all scales |
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The near future will continue to see
accelerating growth in data availability and computing power to support GIS |
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The strategic decision to make now is not
whether, but when and how to use GIS to support decisions |
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Notes