General GIS Information
What Is a GIS?
A geographic information system (GIS) is a computer-based tool for mapping and analyzing things that exist and events that happen on earth. GIS technology integrates common
database operations such as query and statistical analysis with the unique visualization and geographic analysis benefits offered by maps. 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.
Whether siting a new business, finding the best soil for growing bananas, or figuring out the best route for an emergency vehicle, local problems also have a geographical
component. GIS will give you the power to create maps, integrate information, visualize scenarios, solve complicated problems, present powerful ideas, and develop effective solutions like
never before. GIS is a tool used by individuals and organizations, schools, governments, and businesses seeking innovative ways to solve their problems.
Mapmaking and geographic analysis are not new, but a GIS performs these tasks better and faster than do the old manual methods. And, before GIS technology, only a few people had
the skills necessary to use geographic information to help with decision making and problem solving.
Today, GIS is a multibillion-dollar industry employing hundreds of thousands of people worldwide. GIS is taught in schools, colleges, and universities throughout the world.
Professionals in every field are increasingly aware of the advantages of thinking and working geographically.
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What Can GIS Do for You?
Perform Geographic Queries and Analysis
The ability of GISs to search databases and perform geographic queries has saved many companies literally millions of
dollars. GISs have helped reduce costs by :
- Streamlining customer service.
- Reducing land acquisition costs through better analysis.
- Reducing fleet maintenance costs through better logistics.
- Analyzing data quickly, as in this example:
A realtor could use a GIS to find all houses within a certain
area that have tiled roofs and five bedrooms, then list their
Improve Organizational Integration
Many organizations that have implemented a GIS have found that one of its main benefits is improved management of their own organization and resources. Because GISs have the
ability to link data sets together by geography, they facilitate interdepartmental information sharing and communication. By creating a shared database, one department can benefit from the
work of another - data can be collected once and used many times.
Make Better Decisions
The old adage "better information leads to better decisions" is as true for GIS as it is for other information systems. A GIS, however, is not an automated decision making system but a
tool to query, analyze, and map data in support of the decision making process. GIS technology has been used to assist in tasks such as presenting information at planning inquiries, helping
resolve territorial disputes, and siting pylons in such a way as to minimize visual intrusion.
GIS can be used to help reach a decision about the location of a new housing development that has minimal environmental impact, is located in a low-risk area, and is close to a
population center. The information can be presented succinctly and clearly in the form of a map and accompanying report, allowing decision makers to focus on the real issues rather than
trying to understand the data. Because GIS products can be produced quickly, multiple scenarios can be evaluated efficiently and effectively.
Maps have a special place in GIS. The process of making maps with GIS is much more flexible than are traditional manual or automated cartography approaches. It begins with database
creation. Existing paper maps can be digitized and computer-compatible information can be translated into the GIS. The GIS-based cartographic database can be both continuous and scale
free. This allows the creation of map products which are centered on any location, at any scale, and showing selected information symbolized effectively to highlight specific characteristics. The
characteristics of atlases and map series can be encoded in computer programs and compared with the database at final production time. Digital products for use in other GISs can also be
derived by simply copying data from the database. In a large organization, topographic databases can be used as reference frameworks by other departments.
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How GIS works?
A GIS stores information about the world as a collection of thematic layers that can be linked together by geography. This simple but extremely 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.
Geographic information contains either an explicit geographic reference, such as a latitude and longitude or national grid coordinate; or an implicit reference such as an address, postal
code, census tract name, forest stand identifier, or road name. An automated process called geo-coding is used to create explicit geographic references (multiple locations) from implicit
references (descriptions such as addresses). These geographic references allow you to locate features, such as a business or forest stand, and events, such as an earthquake, on the earth's
surface for analysis.
Vector and Raster Models
Geographic information systems work with two fundamentally different types of geographic models - the "vector" model and the "raster" model. In the vector model, information about
points, lines, and polygons is encoded and stored as a collection of x,y coordinates. The location of a point feature, such as a bore hole, can be described by a single x,y coordinate. Linear
features, such as roads and rivers, can be stored as a collection of point coordinates. Polygonal features, such as sales territories and river catchments, can be stored as a closed loop of
The vector model is extremely useful for describing discrete features, but less useful for describing continuously varying features such as soil type or accessibility costs for hospitals.
The raster model has evolved to model such continuous features. A raster image comprises a collection of grid cells rather like a scanned map or picture. Both the vector and raster models for
storing geographic data have unique advantages and disadvantages. Modern GISs are able to handle both models.
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Components of a GIS
A working GIS integrates five key components: hardware, software, data, people, and methods. Hardware is the computer on which a GIS operates. 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.
GIS software provides the functions and tools needed to store, analyze, and display geographic information. Key software components are:
- Tools for the input and manipulation of geographic information
- A database management system (DBMS)
- Tools that support geographic query, analysis, and visualization
- A graphical user interface (GUI) for easy access to tools
Possibly the most important component of a GIS is the data. Geographic data and related tabular data can be collected in-house 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.
GIS technology is of limited value without the people who manage the system and develop plans for applying it to real-world problems. GIS users range from technical specialists who
design and maintain the system to those who use it to help them perform their everyday work.
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A successful GIS operates according to a well-designed plan and business rules, which are the models and operating practices unique to each organization.
GISs are closely related to several other types of information systems, but it is the ability to manipulate and analyze geographic data that sets GIS technology apart. Although there
are no hard and fast rules about how to classify information systems, the following discussion should help differentiate GIS from desktop mapping, computer-aided design (CAD), remote
sensing, DBMS, and global positioning systems (GPS) technologies.
A desktop mapping system uses the map metaphor to organize data and user interaction. The focus of such systems is the creation of maps: the map is the database. Most desktop
mapping systems have more limited data management, spatial analysis, and customization capabilities. Desktop mapping systems operate on desktop computers such as PCs, Macintoshes,
and smaller UNIX workstations.
CAD systems evolved to create designs and plans of buildings and infrastructure. This activity required that components of fixed characteristics be assembled to create the whole structure.
These systems require few rules to specify how components can be assembled and very limited analytical capabilities. CAD systems have been extended to support maps but typically have
limited utility for managing and analyzing large geographic databases.
Remote Sensing and GPS
Remote sensing is the art and science of making measurements of the earth using sensors such as cameras carried on airplanes, GPS receivers, or other devices. These sensors collect
data in the form of images and provide specialized capabilities for manipulating, analyzing, and visualizing those images. Lacking strong geographic data management and analytical
operations, they cannot be called true GISs.
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Database management systems specialize in the storage and management of all types of data including geographic data. DBMSs are optimized to store and retrieve data and many GISs
rely on them for this purpose. They do not have the analytic and visualization tools common to GIS.
Spatial Relationships and Technology
When viewing a map, the map-reader must interpret a variety of points, lines, and other symbols to identify spatial relationships among the geographic entities represented. For
example, you can use a map to find a route from one city to another, or to identify which county contains a feature of interest. The information required to perform these analyses is not explicit
in the map; rather, the map-reader must interpret the required spatial relationships from mapped objects.
In a GIS database, the method by which spatial relationships are explicitly represented is termed topology. Topology is used to describe how linear objects connect, to define areas,
and to identify the areas lying to either side of a linear object. Information about these spatial relationships is stored in a topological data structure and is essential to carry out most GIS
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