Generalisation Procedures

The Elements of Generalisation

There are several processes included in generalisation. A first step, however, is always the selection of the information to be communicated by the map. Then, it is convenient to group the generalisation manipulations performed on the selected data into two main types:

• Semantic generalisation: Based on the initial choice of the relevant information to be presented on the map, semantic generalisation is closely related to classification, and aggregation, as well as symbolisation or exaggeration. Semantic generalisation has a main objective of simplifying the presented data, so at a given (small) scale the complexity of the map does not make the map impossible to read. Semantic generalisation normally takes place before geometric generalisation.
• Geometric generalisation: The complexity of the graphic characteristics of map objects may be still too great to show them clearly, especially if the scale of the map becomes smaller. Therefore, the objective of geometric generalisation is to preserve the important parts of the data and eliminate or simplify the less important ones in order to create a map that will have good visual communication characteristics. Geometric generalisation is closely related to simplification, omission, as well as displacement and orientation.

In this unit, you will learn how and when to use the different generalisation processes. However, as each map provides a different set of requirements, the combination of these fundamental processes will vary from map to map. So a typical workflow of these processes is only shown in the unit Generalisation Methods.

Prerequisites for this unit are knowledge of the generalisation concepts, and the different readability rules used in cartography.

Generalisation is not without danger for ethics: for each data modification, the character or the interpretation of a map can be shifted to a false representation, and brings the map reader to a flawed conclusion. Read the following text from L. Guelke about the danger of data modification to reach more information about this topic. Generalisation_and_ethics.pdf (6KB)