Aims of Generalisation

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.