The basic theory of cartography and GIS mapping (II.)

???? Using GIS technology for cartographic mapping, the ultimate goal is to return to the cartography. The following are some of the classic requirements for map making in cartography:

Maps must conform to reality, to human perception.

???? This is the most basic of the map, each element of the map is shown with the actual entity corresponding, although sometimes in order to highlight the characteristics of the geographical features and moderate exaggeration on the surface, but in general, can not deviate from the real world, and the reality does not match. This is like the eastern and Western painting style, Oriental painting emphasis on freehand brushwork, Western painting emphasis on realism, but no matter which way of expression is the same thing to describe, can make people directly through the map to understand the real world.

In line with the reality of this, GIS has this natural trend, because most of the GIS data is obtained by means of surveying and mapping, itself is with the real world one by one corresponding, but there is a certain difference in proportion, which is like the realism of Western painting. Pure and realistic, it just shows the accuracy of the map, and to be able to direct people to understand the map, easy to accept the content of the map, it also needs to symbolize the data, using abstract symbols (similar to simple strokes of the line) to express content, so that people can see the symbol can think of a geographical element, which is in line with human perception This looks like the freehand effect of Oriental painting. For example, a single mountain can be used with a triangular symbolic reality, while a continuous mountain range can be represented by a graph of three triangular symbols, which is the difference between mountain peaks and mountains. Although the map requires a tool to read the illustrations, it is a good map to be able to better match reading and cognitive habits in symbolic displays.

GIS mapping, more needs to be spent on how to make map expression symbols that conform to human cognition. The overall principle is consistent with the cartography requirements.

Map to Better express the location of various geographical elements of the relationship

???? In the traditional cartography, it is necessary to satisfy the authenticity of the map (that is, the 1th above is in accordance with the reality), so the position of the geographical elements on the map surface must be real, at least the relative position is real, for example, the railway station is on the west side of a highway. In contrast, GIS mapping in the existing data on the map production, spatial location relationship by default is already accurate, why also here to propose geographical features between the location relationship, this is the definition of conceptual differences. Based on GIS mapping, the location relationship between the default geographic features refers to the relationship between map symbols. For example, water conservancy facilities symbols must be labeled on both sides of the river, while the actual GIS data collection of water conservancy facilities (such as hydrological stations, water level station) are on the River Central Line. Again, if the boundaries of the country, if the river divides the national borders, the GIS data acquisition of the border line and the River Center line is overlapping, but the national border line of the symbol must be "jump-painted" way to express. This is the positional relationship of various geographic features on the surface.

???? Therefore, the GIS data in the map making, it is necessary to do a lot of reading and checking the data, and the symbolic rules have certain requirements. The position relationship between the symbols of various elements often brings great difficulty and workload to map making.

Clear and readable surface, with distinct primary and secondary figures

???? Whether it is a traditional mapping or GIS mapping, this is very demanding. What is a clear surface? Is the need to express the geographical elements on the surface, but the layout is neat, do not overlap each other, the map symbol concise but can show all the geographical elements of the species.

???? This is more like a map feature layout. A reasonable layout of symbolic elements can increase the readability of the map. In traditional cartography, typesetting is more convenient, can be arbitrarily modified by the drawing software. But for GIS mapping, more experience and skills are needed. For example, in the process of GIS mapping, it involves labeling the overlap of geographic features (e.g., the name of a museum is labeled with the road), and the symbol's gland for geographical features (such as the bank's symbol has a certain width, which covers its corresponding water surface). A more serious situation is the use of large-scale data to map small-scale maps, such as the use of 1:1000 of data collected back to produce 1:50,000 of the map, which requires a "drawdown" of the map (such as the integration of residential data into block data, not only preserves the distribution of the elements, Also does not lose the reading picture information, but the map surface has become concise), must pass through the data processing to be able to complete. When the map is displayed, you also need to take into account the extent to which the map color is used. It is generally not recommended to use too many colors to render a map, which can make people look dazzling. Cartography on map coloring theory is very suitable for use in GIS mapping, such as four-color mapping, not only using the mathematical topology to distinguish adjacent features, but also reduce the color of the surface.

In order to make the map clear and readable, GIS mapping needs to consider the labeling avoidance, symbol offset, data processing and other work. And this part of the work often requires more map inspection and modification can be perfected.

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Meets topical applications

???? Thematic map applications are very extensive, and basically all of the professional units are in the use of thematic maps. The only feature of thematic maps is to highlight thematic data, and other basic data can be moderately simplified. For example, land use map, forest rotation chart, rainfall distribution map, etc., these are thematic maps. Thematic map to grasp the thematic data display and the basic map display conflict, that is, the primary and secondary relationship must be clear. Furthermore, thematic maps must be implemented according to strict specifications in the map symbol reality and symbolic layout. Therefore, the thematic symbol library needs to be completed before the thematic map is produced. For example, is the Water conservancy thematic symbol library, involving water conservancy facilities, basic topographic elements, watershed level symbols, etc.

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Make a more beautiful map

???? This is actually a new era requirement, but not necessary. In addition to the accuracy and legibility of the beautiful map, it often brings artistry and makes people pleasing to the eye. This is more from the Internet map and the participation of the public. For example, the following two graphs (note: These two pictures are from http://www.arcgisonline.cn/)

These two pictures are very beautiful and artistic, basically people can recognize the first one is the Shanghai Pearl Tower, the second is the Beijing Bird's Nest and Water cube surrounding. Some of the basic requirements of the map are well represented on both charts.

For the production of GIS map, most of them are from two aspects of demand. One is the traditional map production department, these departments need to carry out authoritative map production, and need to print out diagrams. The second is the demand of information department, often need to build GIS application according to business department, need to use GIS tool to publish its map data. It can be seen that the application surface of GIS mapping is very extensive.

The basic theory of cartography and GIS mapping (II.)