By T. Sutton, O. Dassau, M. Sutton
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Additional resources for A Gentle Introduction to GIS
If we wanted to take tourists along a route, such as a scenic route through a mountain pass, it might make sense to use polylines. If we have whole areas that are of tourism interest, such as a nature reserve or a cultural village, polygons might make a good choice. As you can see it's often not easy to know what type of geometry you will need. One common approach to this problem is to make one layer for each geometry type you need. So, for example, if you look at digital data provided by the Chief Directorate : Surveys and Mapping, South Africa, they provide a river areas (polygons) layer and a rivers polyline layer.
Height) and, based on the number of classes you request, create groupings for you. This process is illustrated in Table 3 below. 30 Attribute Value Class and Colour 1 Class 1 2 Class 1 3 Class 1 4 Class 2 5 Class 2 6 Class 2 7 Class 3 8 Class 3 9 Class 3 Table 3: Graduated colour breaks up the attribute value ranges into the number of classes you select. Each class is represented by a different colour. Continuous Colour Symbols: In the previous section on Graduated Colour symbols we saw that we can draw features in discrete groups or classes.
Good examples are 'rivers', 'watersamples' and so on. Illustration 46: After defining our new layer's geometry and attributes, we need to save it to disk. It is important to give a short but meaningful name to your shapefile. 42 Let's recap the process again quickly. To create a shapefile you first say what kind of geometry it will hold, then you create one or more fields for the attribute table, and then you save the shapefile to the hard disk using an easy to recognise name. Easy as 1-2-3! Adding data to your shapefile So far we have only created an empty shapefile.
A Gentle Introduction to GIS by T. Sutton, O. Dassau, M. Sutton