A map is a conventional representation of a landscape.
To understand a map, it is important to know the conventions behind. These conventions
-explained in details in the following chapters- are based on a few principles:
- Scaling: the principle of scaling is to represent the landscape in reduction. Without scaling, maps will be very inconvenient to handle: the map of Windhoek will be a piece of paper of approximately 6 x 10 km - not easy to fit in your pocket !
- Projecting: the surface of the Earth is curved, while the paper used to print the map is flat. It is impossible to perfectly represent a curved surface on a plane (try to flatten an orange peel !), but using complex mathematical functions, it is possible to reach a fairly good approximation.
- Referencing: the position of an object on the surface of the Earth can be precisely defined by its Latitude and Longitude. On a map, this position is translated by coordinates on a reference grid. To fully locate a point in space, its elevation must also be given. Different methods are used to indicate elevation on a map: colours, contour lines, spot heights, etc.
- Selection: not all elements visible in a landscape are represented on a map. For instance, cars are not represented on a city plan, because these features are not located permanently.
- Systematism: if one category of objects is represented on the map, then all objects of the same category must be represented. This principle is sometimes adapted for practical reasons. For instance, the author of the map may decide to represent only the important rivers, etc.
- Consistency: similar objects are represented in a similar way.
- Synchronism: a map is supposed to be a snapshot of the landscape. This means that all elements should correspond to the same situation. This rule is sometimes obliterated, when some sources of information are updated more frequently. For instance, it is quite common to update the representation of the roads more frequently than the relief, as the latter is less supposed to change. In normal circumstances, all information belonging to the same theme (roads, rivers, names, etc.) should be time-consistent, but different themes might be updated at different frequencies.
- Symbolisation: on an aerial photo (witch can be to some extent assimilated to a map), the objects are represented faithfully, but their identification is not always easy, especially for non-specialists. On a map, graphical conventions are used to enhance the readability. For instance, important roads are displayed in bright red colour, churches are represented by an evocative symbol, etc.