Geospatial Information Systems (GIS)
A geographic information system (GIS), or some times referred to as a geospatial information system is a system for capturing, storing, analyzing and managing geographic data and associated attributes which are spatially referenced to the earth. In the strictest sense, it is a computer system capable of integrating, storing, editing, analyzing, sharing, and displaying geographically-referenced information. In a more generic sense, GIS is a tool that allows users to create interactive queries (user created searches), analyze the spatial information, edit data, and present the results of all these operations. Geographic information science is the science underlying the applications and systems, taught as a degree program by several universities.
Geographic information system technology can be used for scientific investigations, resource management, asset management, Environmental Impact Assessment, Urban planning, cartography, criminology, history, sales, marketing, and route planning. For example, a GIS might allow emergency planners to easily calculate emergency response times in the event of a natural disaster, a GIS might be used to find wetlands that need protection from pollution, or a GIS can be used by a company to find new potential customers similar to the ones they already have and project sales due to expanding into that market.
GIS stands for Geographic Information Systems or Geographic Information Science. The abbreviation 'GIS' could mean these meanings interchangeably; though the more commonly assigned meaning to 'GIS' is Geographic Information Systems. Geographic Information Systems deal with Geographic data which is similar to non-Geographic data except that there is a Geographic location associated with each datum of Geographic data. Geographic Information Systems are software used for the effective database storage of geographic data, its transformation of one data format to another, its pictorial or model representation and its analysis and manipulation. Technically, a GIS can be classified into five functional units.
- The Geographic Database functional unit
- The Geographic Data Transformation functional unit
- The Geographic Data Manipulation function unit
- The Geographic Data Analysis function unit
- The Geographic Data Representation function unit
The Geographic Database function of the GIS performs Geographic data storage, data organisation and data retreival tasks. The Geographic Data Transformation function of the GIS performs the task of preparing Geographic data for use within the GIS. Raw or legacy Geographic data is transformed into a Geographic data format supported by the GIS. The Geographic Data Manipulation function of the GIS performs tasks related to finer adjustments and rectification of the Geographical data. For example, an aerial photograph may have the need to be stretched (orthorectified) so that its pixels align with longitude and latitude specifications of the Geometric projection in use. Processes like these must be distinguished from Geographic Data Transformation by the fact that these changes are permanent, more complex and time consuming. The Geographic Data Analysis function of the GIS performs all the tasks of data processing that help the analyst make specific sense out of the Geographic data. For illustration, the histogram function prepares a histogram of the input pixel data of the image and give out a plot that helps the analyst plot important characteristics about the data under processing. The Geographic Data Representation function of the GIS handles the representation of the Geographic data in pictorial or model form for comprehension.
GIS is considered a specialized high-end software, generally used by persons skilled in photogrammetry and GIS processing.
Open Source GIS Tools
- GRASS - the most powerful opensource GIS application
- Natural Resources Database - GIS
- OSSIM - Open Source Software Image Map
- Quantum GIS - A user friendly GIS. An opensource alternative to ArcView.
- SAGA GIS
- Thuban - an Interactive Geographic Data Viewer
- TreeSap - Qualitative Reasoning GIS