The data model represents a set of guidelines to convert the real world (called entity) to the digitally and logically represented spatial objects consisting of the attributes and geometry. The attributes are managed by thematic or semantic structure while the geometry is represented by geometric-topological structure.
There are two major types of geometric data model ; vector and raster model, as shown in Figure 2.1
a. Vector Model
Vector model uses discrete points, lines and/or areas corresponding to discrete objects with name or code number of attributes.
b. Raster Model
Raster model uses regularly spaced grid cells in specfic sequence. An element of the grid cell is called a pixel (picture cell). The conventional sequence is row by row from the left to the right and then line by line from the top to bottom. Every location is given in two dimensional image coordinates ; pixel number and line number, which contains a single value of attributes.