Generalization (cartography)
In the generalization of map content is simplified, so that understanding through retained a map. This is necessary if the realistic and complete reproduction is no longer possible with small map scales . Generalization replaces true-to-scale illustrations with simplified images, symbols or signatures . Information is selected, summarized and what is important is presented in preference to what is unimportant.
For a realistic image, the content of a card would have to be photographically reduced to the point of illegibility. Additional information such as place names cover the map content behind it. Clearly legible map symbols are far larger than the scaled down of the displayed object. They therefore compete with neighboring map characters and map contents for the available space.
Generalization creates a balance between these competing demands for realism, completeness, legibility, variety of information and space requirements.
It is therefore an essential distinguishing feature of the map from a photographic image such as an aerial photo or orthophoto .
An important and widespread example of generalization is the " German General Map ", which has been around since the turn of the 19th and 20th centuries.
Procedure of generalization
When generalizing the map information, several processes are applied simultaneously and, if necessary, also on the same map object.
By selecting , unimportant information is excluded from the display and space is created for what is important. What is “important” depends on the type of card. For overview maps and road maps z. B. only the major and broad streets are shown. In a large-scale topographic map, dirt roads are also selected for display.
The simplification of the representation can start with the topographers surveying the terrain . Small building jumps are not included in the survey or smoothed out when the maps are drawn. In the case of serpentines and meanders , the curves are smoothed for the display and in the case of very small scales they are indicated symbolically.
The Merge especially similar representation creates space and clarity. It is typical to group houses together. In the topographic map, individual houses are still shown at a scale of 1: 25,000. Already at the following scale of 1: 50,000 they are grouped together in house groups. Closed areas are represented by area signatures.
The map image is kept simple by classifying . The classification leads to the formation of categories and thus helps to sensibly limit the scope of the map's character set. The topographic map only needs characters for “coniferous tree” and “deciduous tree” instead of each type of tree. With the classification of cities as "seat of government" by underlining the name, the map receives additional information.
The evaluation serves to emphasize or emphasize an object. This can be additional information, e.g. B. a symbol "worth seeing" for a historical building or the bold type of a name. The cartographic exemption of a map sign z. B. by a prominent border can also serve the evaluation.
The enlargement in comparison to the true-to-scale representation is essential to maintain the legibility of the map. The most common application is widening with the use of signatures for traffic routes.
The targeted displacement is usually necessary as a result of the enlargement. Due to the broadened street signature, the neighboring houses are displaced from their geometrically correct map location. The Middle Rhine Valley provides a prime example of the generalization task of regulating displacement. There are railway lines, federal highways and local roads on both sides of the river, which have to be represented by signatures on small-scale maps. The cartographer has to weigh up whether the Rhine is shown narrower or the Hunsrück smaller. This inevitably leads to contradictions in the small-scale topographic maps: A trigonometric point must be displayed in the correct position on the map so that its coordinates can be read off. Due to the space required by the road and railroad signatures, it appears to be in the middle of the road on the map. In nature, however, it lies on the top of a height of the Rhine that has been displaced on the map.
Reason and time of generalization
The main cartographic elements that require generalization are the scale, the map theme, and the manufacturing process.
The generalization is called scaled if the scale of the map does not allow a detailed reproduction because there is not enough space.
In the subject-related generalization, the type of map information to be displayed requires a simplification and summary. Thematic maps require the information to be presented to be prepared in accordance with the topic and usually use simplified base maps that contain e.g. B. can be derived from topographic maps by generalization. While the generalization process for topographic maps and atlases uses standardized procedures and agreed map symbols in many areas, the generalization process for thematic data is often more extensive. Depending on the topic, the type of presentation of a situation must also be redefined and the type and scope of the font used must be redefined. The point in time at which the data is recorded can play an important role in generalization, for example if the facts to be displayed change permanently, but the map should remain up-to-date for a longer period of time.
The generalization process is called process-related when external conditions force simplifications or restrictions in the recording and processing of cartographic information. That can be B. be cost aspects on the basis of which an estimate is made instead of an exact count. The automated display of the map content on low-resolution graphic displays also requires process-related generalization.
The generalization process accompanies the production of the map from the initial data acquisition to the preparation of the map reproduction on a print template or other display device. The generalization in data collection is known as collection generalization . If you generalize between different models, one speaks of model generalization. The main aim of cartographic generalization is to maintain the minimum dimensions when creating a cartographic model. In the case of cartographic generalization, in particular, the requirement for geometrical correctness is postponed in favor of better legibility.
Automation of generalization for digital maps
Generalization is a weighing process and requires creative skills to design a card with an appealing and harmonious appearance. In the case of thematic maps, innovative approaches are sometimes necessary. In contrast, the automation of the generalization process requires fixed algorithms. The aforementioned generalization processes are therefore examined and classified with regard to their suitability for automation. While the over-wide representation of a street using signatures can be automated well, the positioning of place names is one of the processes that are difficult to automate. However, the rapid growth of digital map applications requires automated processes in the short term. Here, pragmatic and simple approaches are quite appropriate to display the map image on low-resolution screens such as B. to improve navigation systems in the short term.
At the moment, more work is being done on automatic generalization in cartography ( ADV project).
See also
literature
- Friedrich Töpfer: Cartographic generalization . VEB Hermann Haack, Geographisch - Kartographische Anstalt Gotha / Leipzig, 1979, 336 pp.
- Günter Hake: Cartography . Walter de Gruyter, Berlin 1982, ISBN 3-11-008455-4
- Jürgen Bollmann (ed.): Lexicon of cartography and geomatics . Spektrum Akademischer Verlag, Heidelberg 2002, ISBN 3-8274-1056-8