Unit 23 GIS Basic
Unit 23 GIS Basic
Definitions of GIS
“GIS”is an acronym meaning of Geographic Information System , In order to provide a good understanding of GIS , the following two definitions given by Rhind (1989) and the United States Geological Survey(USGS,1997) respectively are presented first.
1. ```a system of hardware , software , and procedures designed to support the capture ,manipulation, analysis , modeling , and display of spatially referenced data for solving complex planning and management problems.
2. ``` a computer system capable of assembling, storing , manipulating , and displaying geographically referenced information , i.e . , data identified according to their location .
GIS books generally adopt the ideas expressed by these two definitions . These two characteristics distinguish GIS from other types of information systems:The word “Geographic”in GIS explains “spatially”where things are such as the location of nations, states ,counties , cities , schools , roads, rivers , lakes , and the list can go on and on . Spatially means where on the earth’s surface an object or feature is located . This can be as simple as the latitude and longitude of a feature . The geographic feature or object can be anything of interest . “Information”in GIS is the “data”or “attribute” information about specific features that we are interested in . The name of the feature , what the feature is, the location of the feature , and any other information that is important . An example could be the name of a city , where it is located , how big it is in square feet(area) , its population , its population in the past . And any other information is important . “System”in GIS is the computer software that is written to help people analyze the data , look at the data and combine it in various ways to show relationships or to create geographic models , A GIS can be made up of a variety of software and hardware tools, as long as they are integrated to provide a functional geographic data processing tool .
As mentioned above, GIS is computer system that links geographic information (where things are) with descriptive information what things are . Unlike a flat paper map, where what you see is what you get , a GIS can present many layers of different information. To use a paper map , all you do is unfold it . Spread out before you is a representation of cities and roads . Mountains and rivers , railroads , and political boundaries . The cities are represented by little dots or circles , the roads by black lines , the mountain peaks by tiny triangles , and the lakes by small blue area similar to the real lakes . A digital map is not much more difficult to use than a paper map . As on the paper map , there are dots or points that represent features on the map such as cities, lines that represent features such as roads and small areas that represent features such as lakes . All this information~~where the point is located , how long the road is, and even how many square miles a lake occupies~~is stored as layers in digital format as a pattern of ones and zeros in a computer . Think of this geographic data as layers of information underneath the computer screen . Each layer represent a
particular theme or feature of the map . One theme could be made up of all the roads in an area .Another theme could represent all the lakes in the same area . Y et another could represent all the cities . These themes can be laid on top of one another , creating a stack of information about the same geographic area . Each layer can be turned off and on , as if you were peeling a layer off the stack or placing it back on . Y ou control the amount of information about an area that you want to see , at any time , on any specific map.
The technology components of a GIS can be explained in terms of hardware , software and human resources . GIS hardware includes : computers , computer configuration/networks , input devices , printers , and storage systems . Computers for GIS usage can be PCs or supercomputers . These computers can be stand-alone units or can be hooked into a network environment . Input devices include digitizers and scanners . Printers and plotters are used to produce a hardcopy map . GIS storage systems include :optical disks , magnetic disks such as a hard drive , floppy disks or magnetic tapes .
GIS software includes both GIS program and special application packages, such as digital terrain modeling and network analysis . The main difference between GIS software programs and desktop mapping programs is the ability of GIS programs to perform spatial analysis. ARC/INFO by Environmental Systems Reacher Institute (ESRII) Inc . Is one of typical examples of GIS software packages . Desktop mapping programs offer many of the same features , as a GIS , but their ability to support spatial analyses are limited . They are developed to satisfy individual user needs for mapping presentations . MapInfo developed by MapInfo Corp is an example of popular desktop mapping program .
Human resources used to operate a GIS typically include : operational staff , technical professional staff , and management personnel . Operational staff are people such as (1) cartographers , who monitor the design of map display , the standards for map symbols and standard map series , (2) data capturers , who converts map into digital form and (3) potential users of a GIS , Technical professional staff include (1) information analysts who solve particular user problems and satisfy their information needs , (2) system administrators , who are responsible for keep ing the system (hardware/software) operational , (3) programmers , who translate the application specifications prepared by the analyst into program and (4) the database administrator , who assist the analysts , programmers and users to organize geographic features into layers, identify source of data , develop coding structures for non-graphics data , and document information about the contents of the database . Management personal include (1) the manager , who monitors the daily performance of the GIS project implementation team and manages the output production as required by the organization and (2) the Quality Assurance Coordinator who manages the output of the final product to ensure that is meets the conversion specification and data acceptance plan .