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A geographic information system (GIS) is a system for managing data that has a spatial specialized form of an information system. In the strictest sense, it is a computer system capable of assembling, storing, manipulating, and displaying geographically-referenced information, i.e. data identified according to their locations, in a database. Practitioners also regard the total GIS as including operating personnel and the data that go into the system.
Geographic information systems technology can be used for scientific investigations, resource management, development planning, cartography and route planning. For example, a GIS might allow emergency planners to easily calculate emergency response times in the event of a natural disaster, or a GIS might be used to find wetlands that need protection from pollution.
History of Development
35,000 years ago, on the walls of caves near Lascaux, France, Cro-Magnon hunters drew pictures of the animals they hunted. Associated with the animal drawings are track lines and tallies thought to depict migration routes. These early records followed the two-element structure of modern geographic information systems: a graphic file linked to an attribute database.
In the 1700s modern surveying techniques for topographic mapping were implemented, along with early versions of thematic mapping, e.g. for scientific or census data.
The early 20th century saw the development of "photo lithography" where maps were separated into layers. Computer hardware development spurred by nuclear weapon research would lead to general purpose computer "mapping" applications by the early 1960s.
The year 1967 saw the development of the world's first true operational GIS in Ottawa, Ontario by the federal Department of Energy, Mines and Resources. Developed by Roger Tomlinson, it was called "Canadian GIS" (CGIS) and was used to store, analyse and manipulate data collected for the Canada Land Inventory (CLI) - an initiative to determine the land capability for rural Canada by mapping various information on soils, agriculture, recreation, wildlife, waterfowl, forestry, and land use at a scale of 1:250,000. A rating classification factor was also added to permit analysis.
CGIS was the world's first "system" and was an improvement over "mapping" applications as it provided capabilities for overlay, measurement, digitizing/scanning, supported a national coordinate system that spanned the continent, coded lines as "arcs" having a true embedded topology, and it stored the attribute and locational information in separate files. Its developer, geographer Roger Tomlinson, has become known as the "father of GIS."
CGIS lasted into the 1970s but took too long to complete, following its initial development, and as such couldn't compete with the various commercial mapping applications being sold by vendors such as Intergraph. The development of micro-computer hardware spurred vendors such as ESRI and CARIS to successfully incorporate many of the CGIS features, combining the 1st generation approach to separation of spatial and attribute information with a 2nd generation approach to organizing attribute data into database structures. The 1980s and 1990s industry growth were spurred on by the growing use of GIS on UNIX workstations and the personal computer. By the end of the 20th century, the rapid growth in various systems had been consolidated and standardized on relatively few platforms and users were beginning to export the concept of viewing GIS data over the Internet, requiring data format and transfer standards.
Techniques used in GIS
Relating information from different sources
If you could relate information about the rainfall of your state to aerial photographs of your county, you might be able to tell which wetlands dry up at certain times of the year. A GIS, which can use information from many different sources in many different forms, can help with such analyses. The primary requirement for the source data consists of knowing the locations for the variables. Location may be annotated by x,y, and z coordinates of longitude, latitude, and elevation, or by other geocode systems like ZIP codes or by highway mile markers. Any variable that can be located spatially can be fed into a GIS. Several computer databases that can be directly entered into a GIS are being produced by government agencies and non-government organizations. Different kinds of data in map form can be entered into a GIS.
A GIS can also convert existing digital information, which may not yet be in map form, into forms it can recognize and use. For example, digital satellite images generated through remote sensing can be analyzed to produce a map-like layer of digital information about vegetative covers.
Likewise, census or hydrologic tabular data can be converted to map-like form, serving as layers of thematic information in a GIS.
Data Representation
GIS data represents real world objects (roads, land use, elevation) with digital data. Real world objects can be divided into two abstractions: discrete objects (a house) and continuous fields (rain fall amount or elevation). There are two broad methods used to store data in a GIS for both abstractions: Raster and Vector.
Raster data consists of rows and columns of cells that store a single value. It is similar to a raster image, but besides just color, the value recorded for each cell may be a categorical class, such as land use, a continuous value, such as rainfall, or a null value if no data is available. The resolution of the raster dataset is its cell width in ground units. Usually cells represent square areas of the ground, but other shapes can also be used. Raster data can be used for representing both fields and objects, with objects being recorded as ....
Vector data uses geometries such as points, lines (a series of point coordinates), or areas (shapes bounded by lines) to represent objects. Examples include property boundaries for a housing subdivision represented as polygons and well locations represented as points. Vectors can also be used to represent continuously varying fields. Contour lines and triangulated irregular networks (TIN) are used to represent elevation or other continuously changing values. TIN's record values at point locations, which are connected by lines to form an irregular mesh of triangles. The face of the triangles represent the terrain surface.
There are advantages and disadvantages to using a raster or vector data model to represent reality. Raster datasets record a value for all points in the area covered which may require more storage space than representing data in a vector format that can store data only where needed. Raster data also allows easy implementation of overlay operations, which are more difficult with vector data. Vector data can be displayed as vector graphics used on traditional maps, whereas raster data will appear as an image that may have a blocky appearance for object boundaries.
Additional non-spatial data can also be stored besides the spatial data represented by the coordinates of a vector geometry or the position of a raster cell. In vector data, the additional data are attributes of the object. For example, a forest inventory polygon may also have an identifier value and information about tree species. In raster data the cell value can stores attribute information, but it can also be used as and identifier that can relate to records in another table.
Data Capture
How can a GIS use the information in a map? If the data to be used are not already in digital form, that is, in a form the computer can recognize, various techniques can capture the information. Maps can be digitized, or hand-traced with a digitizer, to collect the coordinates of features.
Electronic scanning devices will also convert map lines and points to digits.
A GIS can be used to emphasize the spatial relationships among the objects being mapped. While a computer-aided mapping system may represent a road simply as a line, a GIS may also recognize such a road as the border between wetland and urban development, or as the link between Main Street and Blueberry Lane.
Data capture - putting the information into the system - consumes much of the time of GIS practitioners. Identities of the objects on the map must be specified, as well as their spatial relationships. Editing of automatically captured information can also prove difficult. Electronic scanners record blemishes on a map just as faithfully as they record the map features. For example, a fleck of dirt might connect two lines that should not be connected. Extraneous data must be edited, or removed from the digital data file.
A GIS makes it possible to link, or integrate, information that is difficult to associate through any other means. Thus, a GIS can use combinations of mapped variables to build and analyze new variables.
Using GIS technology and water-supplier billing information, it is possible to simulate the discharge of materials in the septic systems in a neighborhood upstream from a wetland. The bills show how much water is used at each address. The amount of water a customer uses will roughly predict the amount of material that will be discharged into the septic systems, so that areas of heavy septic discharge can be located using a GIS.
TODO: remote sensing, areal photo interpretation.
Data Manipulation
Data restructuring can be performed by a GIS to convert data into different formats. For example, a GIS may be used to convert a satellite image map to a vector structure by generating lines around all cells with the same classification, while determining the cell spatial relationships, such as adjacency or inclusion.
Since digital data are collected and stored in various ways, the two data sources may not be entirely compatible. So a GIS must be able to convert geographic data from one structure to another.
Projections, coordinate systems and registration
A property ownership map and a soils map might show data at different scales. Map information in a GIS must be manipulated so that it registers, or fits, with information gathered from other maps. Before the digital data can be analyzed, they may have to undergo other manipulations - projection and coordinate conversions, for example - that integrate them into a GIS.
The earth can be represented by various models, each of which may provide a different set of coordinates (e.g., latitude, longitude, elevation) for any given point on the earth's surface. The simplest model is to assume the earth is a perfect sphere. As more measurements of the earth have accumulated, the models of the earth have become more sophisticated and more accurate. In fact, there are models that apply to different areas of the earth to provide increased accuracy (e.g., North American Datum, 1983 - NAD83 - works well in North America, but not in Europe).
Projection is a fundamental component of map making. A projection is a mathematical means of transferring information from a model of the Earth, which represents a 3 three-dimensional curved surface, to a two-dimensional medium - paper or a computer screen. Different projections are used for different types of maps because each projection particularly suits certain uses. For example, a projection that accurately represents the shapes of the continents will distort their relative sizes.
Since much of the information in a GIS comes from existing maps, a GIS uses the processing power of the computer to transform digital information, gathered from sources with different projections and/or different coordinate systems, to a common projection and coordinate system.
TODO: move to data manipulation
Spatial Analysis with GIS
Data modeling
It is difficult to relate wetlands maps to rainfall amounts recorded at different points such as airports, television stations, and high schools. A GIS, however, can be used to depict two- and three-dimensional characteristics of the Earth's surface, subsurface, and atmosphere from information points.
For example, a GIS can quickly generate a map with lines that indicate rainfall amounts.
Such a map can be thought of as a rainfall contour map. Many sophisticated methods can estimate the characteristics of surfaces from a limited number of point measurements. A two-dimensional contour map created from the surface modeling of rainfall point measurements may be overlaid and analyzed with any other map in a GIS covering the same area.
Topological modeling
In the past 35 years, were there any gas stations or factories operating next to the swamp? Any within two miles and uphill from the swamp? A GIS can recognize and analyze the spatial relationships among mapped phenomena. A GIS can determine conditions of adjacency (what adjoins what), containment (what encloses what), and proximity (how close something is to something else).
Networks
If all the factories near a wetland were accidentally to release chemicals into the river at the same time, how long would it take for a damaging amount of pollutant to enter the wetland reserve? A GIS can simulate the route of materials along a linear network. It is possible to assign values such as direction and speed to the digital stream and "move" the contaminants through the stream system.
Also use to find shortest routs through a road network
Cartographic Modelling
Powerful analysis techniques with raster data.
Vector Overlay
Spatial Statistics
Using geostatistics to predict fields from points.
Point pattern analysis.
GeoCoding
Calculating locations from street addresses.
Reverse geocoding
Converting a given latitude and longitude into a human readable description of a location, usually a street address.
Data output and cartography
Cartography is the design and production of maps, or visual representations of spatial data. The vast majority of modern cartography is done with the help of computers, usually using a GIS. Most GIS software gives the user substantial control over the appearance of the data.
Cartographic work serves two major functions. First, it can be an important part of
A critical component of a GIS is its ability to produce graphics on the screen or on paper that convey the results of analysis to the people who make decisions about resources. Wall maps and other graphics can be generated, allowing the viewer to visualize and thereby understand the results of analyses or simulations of potential events. Web Map Servers facilitate distribution of generated maps via the web technology.
In addition to visual representations of the data,
Other database information can be generated for further analysis or use. A list of all addresses within 1 mile of a toxic spill for instance.
Graphic display techniques
Traditional maps are abstractions of the real world, a sampling of important elements portrayed on a sheet of paper with symbols to represent physical objects. People who use maps must interpret these symbols. Topographic maps show the shape of land surface with contour lines; the actual shape of the land can be seen only in the mind's eye.
Today, graphic display techniques such as shading based on altitude in a GIS can make relationships among map elements visible, heightening one's ability to extract and analyze information. For example, two types of data were combined in a GIS to produce a perspective view or a portion of San Mateo County, California.
- The digital elevation model, consisting of surface elevations recorded on a 30-meter horizontal grid, shows high elevations as white and low elevation as black.
- The accompanying Landsat Thematic Mapper image shows a false-color infrared image looking down at the same area in 30-meter pixels, or picture elements, for the same coordinate points, pixel by pixel, as the elevation information.
A GIS was used to register and combine the two images to render the three-dimensional perspective view looking down the San Andreas Fault, using the Thematic Mapper image pixels, but shaded using the elevation of the landforms. The GIS display depends on the viewing point of the observer and time of day of the display, to properly render the shadows created by the sun's rays at that latitude, longitude, and time of day.
GIS software
Computer-aided design (CAD)
Wikipedia articles on GIS software
MapInfo
MapInfo is a software company that integrates software, data and services to help customers realize greater value from location based information and drive more insightful decisions using their range of GIS software platforms.
www.mapinfo.com
ESRI
Please see www.SierraSoft.com you can find a SITIO (GIS)
The future of GIS
Many disciplines can benefit from GIS techniques. An active GIS market has resulted in lower costs and continual improvements in the hardware and software components of GIS. These developments will, in turn, result in a much wider application of the technology throughout government, business, and industry.
OGC Standards
Open Geospatial Consortium (OGC)
Global Change and Climate History Program
Maps have traditionally been used to explore the Earth and to exploit its resources. GIS technology, as an expansion of cartographic science, has enhanced the efficiency and analytic power of traditional mapping. Now, as the scientific community recognizes the environmental consequences of human activity, GIS technology is becoming an essential tool in the effort to understand the process of global change. Various map and satellite information sources can combine in modes that simulate the interactions of complex natural systems.
Through a function known as visualization, a GIS can be used to produce images - not just maps, but drawings, animations, and other cartographic products. These images allow researchers to view their subjects in ways that literally never have been seen before. The images often are equally helpful in conveying the technical concepts of GIS study-subjects to non-scientists.
zxc
Adding the element of time
The condition of the Earth's surface, atmosphere, and subsurface can be examined by feeding satellite data into a GIS. GIS technology gives researchers the ability to examine the variations in Earth processes over days, months, and years. As an example, the changes in vegetation vigor through a growing season can be animated to determine when drought was most extensive in a particular region. The resulting graphic, known as a normalized vegetation index, represents a rough measure of plant health.
Working with two variables over time will allow researchers to detect regional differences in the lag between a decline in rainfall and its effect on vegetation.
GIS technology and the availability of digital data on regional and global scales enable such analyses. The satellite sensor output used to generate the vegetation graphic is produced by the Advanced Very High Resolution Radiometer or AVHRR. This sensor system detects the amounts of energy reflected from the Earth's surface across various bands of the spectrum for surface areas of about 1 square kilometer. The satellite sensor produces images of a particular location on the Earth twice a day. AVHRR is only one of many sensor systems used for Earth surface analysis. More sensors will follow, generating ever greater amounts of data.
GIS and related technology will help greatly in the management and analysis of these large volumes of data, allowing for better understanding of terrestrial processes and better management of human activities to maintain world economic vitality and environmental quality.
References and further reading
See also: cartography, remote sensing, Open GIS Consortium, GRASS GIS, geoinformation, geodesy, geoinformatics
Textbooks
- Heywood, I., Cornelius, S., and Carver, S. 1998. An Introduction to Geographical Information Systems. Andison Wesley Longman.
- Longley, P.A., Goodchild, M.F., Maguire, D.J. and Rhind, D.W. (2001): Geographic Information Systems and Science. Chichester: Wiley.
- Worboys, Michael, and Matt Duckham. 2004. GIS: a computing perspective. Boca Raton: CRC Press. [1] (http://worboys.duckham.org)
External links
- Space Applications for Development (http://topics.developmentgateway.org/space)
- NCGIA Core Curriculum in GIS (http://www.geog.ubc.ca/courses/klink/gis.notes/ncgia/toc.html) - lecture notes for educators written by the National Center for Geographic Information Analysis (NCGIA).
- Open GIS Consortium (http://www.opengis.org)
- FreeGIS (http://freegis.org/)—Free Software and Geo-Data.
- spatiallink_org (http://www.spatiallink.org/)—Linking GIS Volunteers Through Chat, Wiki, Blog and Other Tools
- FreeGISBook (http://www.eogeo.org/Projects/projects_wiki/FreeGISBook)—WiKi project to develop a comunity based book and documents on free GIS programs and open standards.
- Federal Geographic Data Committee (http://www.fgdc.gov/)—United States federal government standards agency
- Edinburgh GIS Server Home (http://www.geo.ed.ac.uk/home/gishome.html)
- Geoplace (http://www.geoplace.com)—free source of GIS Industry information
- SAGA (http://geosun1.uni-geog.gwdg.de/saga/html/index.php)—free GIS software under the GNU General Public License
- Giiki Wiki GIS (http://www.andysocial.com/wiki/index.php/Imagery)—English-language wiki for Geographic Information Systems and amateur imagery/IMINT.
- PostGIS (http://postgis.refractions.net)—spatial extensions for the open source Postgres database.
- GRASS GIS (http://grass.itc.it/)—well-established open-source GIS software
- Geoserver (http://geoserver.sf.net/)—an open-source portal for spatial data
- TaGISViewer (http://www.tagisviewer.co.uk/)—Free Temporal GIS viewer
- MiraMon (http://www.creaf.uab.es/miramon/)— MiraMon GIS & RS software
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