The accuracy of the map as a whole depends on the accuracy of measurements (position, height and shape) and the accuracy of drawing. The relative positions of elements on an Orienteering map must be consistent with those obtained using a compass.
A feature must be positioned with sufficient accuracy to ensure that a competitor using compass
and pacing will perceive no discrepancy between map and ground.
Absolute height accuracy is of little significance on an orienteering map. On the other hand, it is important that the map shows as correctly as possible the relative height difference between neighbouring features.
An accurate representation of shape is of great importance for the orienteer, as a detailed and sometimes exaggerated picture of the landform is an essential precondition for map reading. However, you should avoid including too many small details so as not to hide the main elements.
Accurate representation of shape is of great importance for the orienteer, because a correct, detailed and sometimes exaggerated picture of the landform is an essential precondition for map reading. However, the inclusion of a lot of detail must not disguise the overall shape. This means that form line usage must be limited to an absolute minimum (e.g. form lines with a shape that can be deduced from the neighbouring contours shall not appear on the map) and insignificant contour detail must be removed.
Generalization and legibility
Good orienteering terrain contains a large number and a great variety of features. Those which are most essential for the competitor must be selected and presented on the orienteering map. To achieve this, in such a way that the map is legible and easy to interpret, generalisation must be employed. There are two phases of generalisation: selective generalisation and graphical generalisation.
Selective generalisation is the decision as to which detail and features should be presented on the map. Two important considerations contribute to this decision: the importance of the feature from the competitor’s point of view, and its influence on the legibility of the map. These two considerations will sometimes be incompatible, but the demand for legibility must never be relaxed in order to present an excess of details and features on the map. Therefore, it will be necessary at the survey stage to adopt minimum sizes for many types of detail. These minimum sizes may vary somewhat from one map to another according to the amount of detail in question. However, consistency is one of the most important qualities of the orienteering map.
Graphical generalization can greatly affect the clarity of the map. Simplification, displacement and exaggeration of dimensions are used for this purpose.
Legibility requires that the size of symbols, line thicknesses and spacing between lines be based on the perception of normal sight in daylight. In devising symbols, all factors except the distance between neighbouring symbols have been considered.
The size of the smallest feature which will appear on the map depends partly on the graphical qualities of the symbol (shape, format and colour) and partly on the position of neighbouring symbols. With immediately neighbouring features which take up more space on the map than on the ground, it is essential that the correct relationships between these and other nearby features are also maintained.
Content adapted from “ISOM – International Specification for Orienteering Maps”