Exemption (cartography)
In cartography, the term exemption is used to describe the removal of disruptive parts of the map in the edge area and background of an outstanding map element in order to ensure its readability by maintaining its clear contour.
In particular, text elements and signatures are exempted if a background of the same color or less contrasting would impair the recognizability. The release can also be done by contouring the outstanding element. The element. z. B. a letter in a lettering is then given a border that contrasts with the font color.
The background element is partially erased by the exemption. Card information is lost in the process. Therefore, the exemption in cartography is limited to what is necessary. An exemption is not required if there is sufficient color and brightness contrast. In this way, bodies of water (blue) can simply be overprinted with situation descriptions (black) without the situation description losing legibility. Contour lines (brown) must be deleted in the edge area of their associated height information (also brown) so that the writing does not blur with the line and thus becomes difficult to read.
The exemption is also taken into account in the cartographic generalization .
Procedure
The exemption of map elements is basically a complex process, since the exemption work does not have to be carried out on the element to be exempted itself, but on the background element. Due to the manufacturing process for maps, these elements are usually on different drawing levels (analog: foil; digital: layer). They must therefore be brought together before the exemption and then separated again.
Copy-technical exemption
In the conventional production of maps, even with the same printing color, the information is processed separately according to its type (e.g. body of water and lettering) on different foils. A laborious copying process is then required for exemption. The figure shows a typical process using the example of the exemption of the labeling of contour lines.
Procedure for digital maps
The release is easier by contouring the element to be released with a border in a contrasting color or in the color of the background. This method is particularly suitable for automation. It works reliably with cards that are created from only a few colored foils. In the case of maps based on digital data ( vector data ), this process can be taken over directly by the software. For this purpose, a border (buffer) is generated around the map element to be released, which contains the color of the release. Instead of a precise shape contouring, a simpler rectangular or block contouring is accepted for reasons of software simplification .
But also in the digital map production process there are cartography systems which, for the preparation of the vector map data for prepress, release the labeling elements on only explicitly specified map elements, this even on the later same color film (e.g. text black is released against the railway line black, but not compared to black grid settlement area ).