Cartographic generalisation is born of the necessity to communicate. As it
is not possible to communicate map information at 1:1 scale, generalisation has many
aims.
The following aims can also be considered as generalisation rules.
- Structure: The map content is well structured.
- The estimation of map content priorities has to be adapted to the mapscale and to the intended purpose.
- The objects have to be classified according to clear and reasonable criteria.
- The grouping of objects has to be logical.
- Legend: Expressive and associative symbols constitute the base for clear map communication.
- The size and the form of the symbols are adapted to the other symbols and to the reality.
- Generalisation level: The level of generalisation implies simplification and detailing.
- A low level of generalisation signifies a high information density and a fine structured map.
- A high level of generalisation signifies a low information density and a thick structured map.
- The level of generalisation varies according to the purpose and to the mapscale.
- The level of generalisation is carefully defined.
- The level of generalisation affects the legend and the symbols.
- Selection of objects: The objects selection complies with the map purpose.
- The objects selection complies with the mapscale and with the intended purpose.
- The objects that are visible in reality (e.g. houses) are completed with non-visible objects as borders or labelling.
- Accuracy of objects: The optimal accuracy of the objects regarding position and form is reached. However, the visual placement
of objects is more important than the geometrical accuracy.
- Displacing objects is only needed for raising the legibility and for clarification.
- The symbols of visible objects (in reality) have a high accuracy.
- The symbols of non-visible objects (in reality) have a limited accuracy.
- Object displacement is necessary, and the neighbouring objects are adapted.
- TThe form accuracy is only limited by the good legibility and the respect proportions demand.
- The contour lines are not treated as a single line, but are adjusted to the correct reproduction of the ground structure on
each other.
- Reality accuracy: Indeed, the reality is revised and changed, but is still, as far as possible, represented truthfully.
- All objects present in the map really exist.
- Appropriate legend symbols are assigned to the objects.
- Labelling is correctly raised, written and assigned.
- Legibility of the map elements: The map must be readable without auxiliary means (e.g. magnifying glass), and in bad conditions.
- Good legibility is conditioned to the respect of the graphical minimal dimensions (sizes and distances) of the symbols.
- Graphical minimal dimensions leads to an unscaled representation, i.e. to an enlargement of the dimensions scale.
- Graphical readability rules support legibility.
- Graphical representation of the objects: Map content is adapted, legible and graphically convincing.
- Legend is credible and exact.
- The generalisation of the forms and line symbols respect the most exceptional forms and eliminates the small and fortuity
ones.
- The quantitative generalisation from strewn objects (e.g. houses) respects the density of objects in reality.
- The relations and dependencies of objects in reality (e.g., streets, ways, waters, contour lines, etc.) are carefully considered.