GEOGRAPHIC INFORMATION SYSTEM

1. GEOGRAPHIC INFORMATION SYSTEM • GIS are tools that allow for the processing of spatial data into information, generally information tied explicitly to, and used to make decision about, some portion of the earth. • There is no absolutely agreed upon definition of a GIS

2. COMPUTER ASSISTED CARTOGRAPHIC (CAC) SYSTEMS • Computer systems designed to create maps from graphical objects combined with descriptive attributes, are excellent for display, but generally lack the analytical capabilities of GIS. • Input, design, and output of mappable data, rather than working through myriad analytics of the GIS to produce a simple map.

3. COMPUTER ASSISTED DRAFTING (CAD) • A computer system developed to produce graphic images but not normally tied to external descriptive data files • It would not be as easy to use for producing maps as would CAC, nor would it be capable of analysing maps

4. DEFINITION OF GIS • A computer system for collecting, checking, integrating and analysing information related to the surface of the earth (Rhind 1988)

5. DEFINITION OF GIS • A data input sub-system that collects and pre-processes spatial data from various sources. This sub-system is also largely responsible for the transformation of different types of spatial data. • A data storage and retrieval sub-system that organises the spatial data in a manner that allows retrieval, upgrading and editing.

6. DEFINITION OF GIS • A data manipulation and analysis sub-system that performs task on the data, aggregates and desegregates estimates parameters and constrains and performs modelling functions. • A reporting sub-system that displays all or part of he database in tabular graphic or map form

7. MAPS Data Collection: aerial photos, surveys, etc. Data processing: aggregation, classing, etc.; linear process Map production: final step except for reproduction and dissemination Map reproduction GIS Data collection:aerial photos, surveys,etc. Data processing: aggregation, classing, plus analysis; circular process Map production: not always final step;normally one map used to produce still more Map reproduction COMPARISON OF CARTOGRAPHIC PROCESS AS APPLIED TO TRADITIONAL CARTOGRAPHY AND GIS

8. MAP Input: recorded (compiled) on paper from a collected source Points Lines Areas GIS Input:”encoded” into the computer from a collected source Points Lines Areas ANALOG VERSUS DIGITAL GISA COMPARISON OF INPUT SUBSYSTEM FUNCTIONS

9. MAP Sources Aerial photography Digital remote sensing Surveying Visual descriptions Census data Statistical data, etc. GIS Sources Same as map data Digital line graph (DLG) Digital elevation models (DEM) Digital orthophotoquads Other digital databases ANALOG VERSUS DIGITAL GISA COMPARISON OF INPUT SUBSYSTEM FUNCTIONS

10. MAP Points, lines, and areas are drawn on paper with symbols Retrieval is simply a matter of map reading GIS Points, lines and areas are stored as grid cells or coordinate pairs and pointers in computer Attribute tables are associated with coordinate pairs retrieval requires efficient computer search techniques ANALOG VERSUS DIGITAL GISA COMPARISON OF STORAGE AND RETRIEVAL SUBSYSTEM FUNCTIONS

11. MAP Requires rulers, planimeters, compass, and other tools all used by the human analyst Restricted to the data as they are aggregated and represented on the paper map GIS Uses the power of the computer to measure, compare, and describe contents of the database Allows ready access to the raw data and allows aggregation and reclassification for further analysis ANALOG VERSUS DIGITAL GISA COMPARISON OF ANALYSIS SUBSYSTEM FUNCTIONS

12. MAP Graphic device only many forms of maps Modifications can include cartograms, etc. GIS The map is only one type of GIS output With minor exception, GIS offers same options as traditional hand-drawn maps Also includes tables, charts, diagrams, photographs, etc. ANALOG VERSUS DIGITAL GISA COMPARISON OF REPORTING AND OUTPUT FUNCTIONS

13. A TAXONOMY OF INFORMATION SYSTEMS