Classification of geographical symbols

1, according to the geometric properties of the map, can be divided into point symbols, line symbols and area symbols.

Point symbol means that the symbol has the nature of point, regardless of the size of the symbol, it is actually located by the concept of point, and the area of the symbol has no real area significance;

Linear symbols mean that they have positioning significance in the extension direction, regardless of their width.

Regional symbols have actual two-dimensional characteristics. They are located by faces, and their area shapes are consistent with the actual area shapes of the objects they represent.

The positioning of points and lines can be accurate or generalized.

The point, line and surface features of symbols are not necessarily related to the distribution of drawing objects. Although in general, people always seek to express the point, line and surface features of objects with symbols with corresponding geometric properties, it is not always possible to do so, because what symbols are used to express objects depends on both the scale of the map and the technical scheme of organizing map elements. Rivers can be represented as surfaces on large-scale maps, but only as lines on small-scale maps; Cities are represented as regions on large-scale maps, but as points on small-scale maps. Because of the need of organizing elements on the map, area elements can also be represented by point and line symbols. For example, point symbols are used to represent the property characteristics of the whole area (district statistical map, point value symbol, positioning map); Use isolines to represent plane objects, etc.

2. According to the relationship between symbols and map scale, symbols can be divided into proportional symbols, non-proportional symbols (non-proportional symbols) and semi-proportional symbols.

Whether a drawing object can be represented by an area shape similar to the field according to the map scale depends on the area size of the object itself and the map scale size. Only when the width or area of the drawing object can still be kept within the range allowed by the graphic clarity under the condition of a certain proportion, it is possible to use the scale symbol. Proportional symbols are mainly plane symbols; Non-proportional symbols are mainly dot symbols; And the semi-proportional symbol refers to the linear symbol. With the reduction of map scale, some proportional symbols will gradually become semi-proportional symbols or non-proportional symbols, so the non-proportional symbols will increase relatively, while the proportional symbols will decrease relatively.

3. According to the geographical scale represented by symbols, symbols can be divided into qualitative symbols, hierarchical symbols and quantitative symbols.

In principle, traditional map symbols can only show four characteristics of drawing objects: shape, nature, quantity and position. The shape is distinguished by the image of the symbol, and the position is determined by the positioning of the symbol. If the symbol mainly reflects the nominal scale of the object, that is, the difference in nature, it is a "qualitative symbol." Although scale symbols can reflect the actual size of an object, this size is naturally determined by the shape of the object on the map, so most common map symbols are qualitative symbols except digital notes. Symbols (including interval scale and proportional scale) that mainly represent the quantitative characteristics of objects are called "quantitative symbols". All quantitative symbols must be given a proportional relationship (not map scale) on the map, and their values can be estimated or measured through this proportional relationship. The symbol representing the order scale only represents the approximate order of large, medium and small, so it belongs to the "grade symbol". Some level symbols on the map are related to the corresponding quantities through illustrations, which have actually become quantification.

4. According to the shape characteristics of symbols, symbols can be divided into geometric symbols, artistic symbols, linear symbols, area symbols, chart symbols, text symbols and color gamut symbols. This is to classify symbols according to different image forms and emphasize the image characteristics of symbols.

"Geometric symbol" refers to a relatively simple symbolic symbol composed of basic geometric figures; "Artistic symbols" refer to artistic symbols similar to the objects of expression, which can be divided into "pictographic symbols" and "perspective symbols". The "regional symbol" can be composed of various structural patterns or colors, but they are different in visual form, so the regional color can be called "color gamut symbol". "Chart symbol" mainly refers to the number symbol that reflects the concept of the number of objects, and is mostly composed of relatively simple geometric figures; The characters themselves are symbols. Although the characters on the map still retain their original attributes, they have the spatial characteristics of the map, so they are undoubtedly a special form of map symbols.