Geospatial Information Systems (GIS)
GIS (Introduction) 
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.