FUNCTIONS OF GIS:
                                  
                                    The Functions of GIS describe the steps that have to be taken to implement a GIS
. These steps have to be followed in
                                    order to obtain a systematic and efficient system. The steps involved are:

                                   
 I)
Data Capture:

                                                     
Data used in GIS often come from many sources. Data sources are mainly obtained from Manual Digitization and
                                        Scanning
of aerial photographs, paper maps, and existing digital data sets. Remote-sensing satellite imagery and
                                        GPS are promising data input sources for GIS.

                                        In this stage Digitization
(A conversion process which converts paper maps into numerical digits that can be stored in the
                                        computer. Digitizing simplifies map data into sets of points, lines, or cells that can be stored in the GIS computer )
is carried
                                        out. There are two basic methods of Digitization : Manual Digitizing & Scanning.


                                  
 II) Data Compilation:

                                        Following the digitization of map features, the user completes the compilation phase by relating all spatial features to their
                                        respective attributes
, and by cleaning up and correcting errors introduced as a result of the data conversion process. The end
                                        results of compilation is a set of digital files, each accurately representing all of the spatial and attribute data of interest
                                        contained on the original map manuscripts. These digital files contain geographic coordinates for spatial objects (points, lines,
                                         polygons, and cells) that represent mapped features.


                                   III)
Data Storage (GIS Data Models):

                                       
Once the data have been digitally compiled, digital map files in the GIS are stored on magnetic or other digital media. Data
                                        storage is based on a Generic Data Model that is used to convert map data into a digital form. The two most common types
                                        of data models are Raster and Vector. Both types are used to simplify the data shown on a map into a more basic form that
                                        can be easily and efficiently stored in the computer.
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