The functions above can largely be running a Geographic Information System has the ability to mendepskripsikan geographic data. Basically, Geographic Information Systems (GIS) can receive the data of three components, namely:
1) Data spatial / geographic data associated with a particular position coordinates.
2) non-spatial data (attributes) that are not related to the position in the form of certain themes, such as color, texture, soil, and so on.
3) The relationship between spatial data and data attributes corresponding time.
Sub Systems SIG
Geographic Information Systems (GIS) can be decomposed into several subsystems:
1) Data Input [data capture module – Gistut94]. Responsible for collecting and preparing the spatial and attribute data from various sources. Besides responsible in converting or transforming the original data format into a format that can be used by SIG.
2) Data Output [display modules and reporting – Gistut94]. Displays output all or part of database in the form of softcopy or hardcopy (tables, graphs, and maps).
3) Data Management [subsystem storage and retrieval – Demers97].
Organize spatial and attribute data into the database so easily to be called, updated and edited.
4) Data Manipulation and Analysis. Specifies the information that can be generated by the SIG. In addition, the data model to generate the expected information.
Figure 7. Sub GIS system
One source of data is vitally required input data from a map, so that the data conversion components of maps to digital data are the main components in the system data base in GIS. This process is called Digitizing Map. Digitization is the conversion of analog data into digital data or transfer of map elements (point, line, area) into a series of coordinates or coordinates associated with a code indicating the meaning of the elements.
All data entered on the median strip of paper (papertape) or magnetic tape (magnetic tape). (Aryono P., 1989). At the time of digitization need their code on each feature to be digitized. The coding is intended that the map image in digital form can be converted to digital mapping purposes through editing (Benny J Hendry S, et al, 1987). Digitizer board in the form of a table grid which is a series of electrical conductors to state any position point to the coordinates X and Y.
Because the grid are conductors of electricity, then the cursor is used in the form of a coil which is centered on the cross-threads. When recording a kooordinat point will produce currents that result in a magnetic field and cause the induced voltage in the circuit konduktr electricity grid. Encoder in digitizer will transform electrical pulses into X and Y coordinates (Aryono P, 1989).