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General purpose geographic
information systems essentially perform six processes or tasks:
Input
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.
Modern GIS technology can automate this process fully for large projects using scanning technology; smaller jobs may require some manual digitizing (using a digitizing table). Today many types of geographic data already exist in GIS-compatible formats. This data can be obtained from data suppliers and loaded directly into a GIS.
Manipulation
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. For example, geographic information is available at different scales
(detailed street centerline files; less detailed census boundaries; and postal
codes at a regional level). Before this information can be integrated, it must
be transformed to the same scale (degree of detail or accuracy). This could be a
temporary transformation for display purposes or a permanent one required for
analysis. GIS technology offers many tools for manipulating spatial data and for
weeding out unnecessary data.
Management
For small GIS
projects it may be sufficient to store geographic information as simple files.
However, when data volumes become large and the number of data users becomes
more than a few, it is often 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.
There are many different designs of DBMSs, but in GIS the relational design has been the most useful. In the relational design, data is stored conceptually as a collection of tables. Common fields in different tables are used to link them together. This surprisingly simple design has been so widely used primarily because of its flexibility and very wide deployment in applications both within and without GIS.
Query and Analysis
Once you have a functioning GIS containing your geographic information, you can
begin to ask simple questions such as
And analytical questions such as
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 GISs have many powerful analytical tools, but two are especially important.
Proximity Analysis
To answer such questions, GIS technology uses a process called buffering to determine the proximity relationship between features.
Overlay Analysis
The integration of different data layers involves a process called overlay. At
its simplest, this could be a visual operation, but analytical operations
require one or more data layers to be joined physically. This overlay, or
spatial join, can integrate data on soils, slope, and vegetation, or land
ownership with tax assessment.
Visualization
For many types of geographic operation the end result is best visualized as a
map or graph. Maps are very efficient at storing and communicating geographic
information. While cartographers have created maps for millennia, GIS provides
new and exciting tools to extend the art and science of cartography. Map
displays can be integrated with reports, three-dimensional views, photographic
images, and other output such as multimedia.
 This Homepage was prepared by Kenneth F. Hambrick, Polk County Coordinator. Contact at E-Mail address:
webmaster@pcoem.org for additional information about our program.
The
information contained in this Homepage is considered public
domain and the Office of Emergency Management encourages
interested persons to utilize any portions of it that might be of educational
benefit or enhance their local programs. |
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