GIS are very important knowledge systems in land-use planning. They are used widely for multiple purposes in the process. A GIS can be described in many different ways but all descriptions deal with georeferenced or spatial data. Standard (commercial) software or specific applications are available for dealing with these spatial data . Within GIS the real world and its elements are transformed and formalized into spatial data, which then are processed into information from which results are presented. A GIS can be cell based or vector based. In the cell-based systems, all data are stored in grids. The grids together form one layer in which an area of the real world is represented. In different layers (maps) different kinds of data can be stored. The size of the grids defines the accuracy of the representation, smaller grids (grids that represent a smaller piece of the modeled area) give a better representation of reality than larger grids.
In the vector-based systems the data are stored as points, polygons, and lines. In this format the real world can be represented more accurately. A real point can be depicted as a point and a line as a line. This is not possible in a grid-based format. Points and lines then are depicted as a small area of a certain size, namely the size of one (point) or more cells (lines). Figure 2.4 shows how points, lines, and polygons are represented in grid-based and vector-based formats. Just as in the grid-based format, different sorts of information can be stored in different maps in vector-based formats. This structure of the GIS allows different kinds of information to be recalled and combined.
A GIS can be very useful when a large amount of data must be gathered and stored. With a GIS, this information can be retrieved and processed more easily than when it has to be done manually. It is especially helpful in performing land suitability analyses, described in step 5 of the planning process.
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