Some desktop GIS now support ruled based symbology as a method of rendering a vector layer. If your GIS supports this option you can convert a vector layer from simple points, lines and polygons into something much more meaningful.
Here is an Ordnance Survey sample prior to applying the rule based option. As you can see the layer shows a plain black and white polygon map without any of the features being differentiated depending upon their underlying layer attribute data.
Ordnance Survey sample map. (Copyright OS)
Using the rule based option enables us to select columns from the attribute table and use them to render the layer. This is achieved by assigning relevant colours to each individual attribute type according to predefined colouring rules. Some attributes will involve more choices than others. This is where using the AND and OR functions ensure that the correct attributes are rendered according to the rules we have decided upon.
Attribute data table highlighting descGroups, descrTerms and make columns
Applying these rules to our map in this example creates the layer in the correct colours according to OS rules. Having created the rules it also important to save them to a file so that they can be recalled as required.
Having applied the above rules based option our map is now rendered as in the following example.
Ordnance Survey sample map (Copyright OS)
If you would like to further explore how GIS could help your organisation jps services offers one and two day training courses in QGIS, ArcGIS and MapInfo.
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