Large-scale topographic mapping

Features refer to natural or man-made objects on the ground, such as lakes, rivers, oceans, houses, roads and bridges. Geomorphology refers to the ups and downs of the surface, such as mountains, hills and plains. Features and landforms are collectively called geomorphology. Topographic map is the orthographic projection of the plane position and elevation of ground objects and landforms with specified symbols according to a certain proportion.

1 topographic map scale definition-the ratio of the straight line length d on the map to the corresponding horizontal distance d on the ground.

Important form

Digital scale

The general numerator is 1, and the denominator is a relatively large integer. Such as digital scale1:500 >:1:1000.

Topographic maps with scales of 1:500, 1: 1000, 1:2000 and 1:5000 are called large-scale topographic maps.

Topographic maps with scales of 1: 10000, 1: 25000, 1: 50000, 1: 10000 are medium-scale topographic maps.

Topographic maps with scales of1:200,000,1:500,000,1:/0,000 are called small-scale topographic maps.

China stipulates 1:5000, 1: 1, 000, 1:25000, 1:50000, 1: 1 000. Medium-scale topographic map is the basic map of the country, which is mapped by the national professional surveying and mapping department. At present, aerial photogrammetry is used for mapping, and small-scale topographic maps are generally compiled from medium-scale maps. However, cities and engineering construction generally need large-scale topographic maps, and topographic maps with scales of 1:500 and 1: 1000 are generally measured by flatbed, theodolite or total station.

2 Large-scale topographic map schema topographic map symbols: symbols and methods to represent features and landforms. The topographic map of a country is unified and belongs to the national standard. There are three kinds of symbols in topographic map schema: feature symbol, landform symbol and annotation symbol.

(1) characteristic symbol? The symbols of ground objects are divided into proportional symbols, non-proportional symbols and semi-proportional symbols. Proportional symbol

The scale can be reduced according to the drawing scale, and the ground object symbols drawn with the specified symbols are called scale symbols, such as houses, wide roads, rice fields, flower beds, lakes, etc.

Non-proportional symbol

Some ground objects, such as triangle points, traverse points, leveling points, independent trees, street lamps, manholes, etc. , with a small outline, its shape and size can not be drawn on the map according to the scale of topographic map, so its actual size is not considered, but expressed by specified symbols. This symbol is called non-proportional symbol.

Semi-proportional symbol

For some strip-shaped extension features, such as paths, communication lines, pipes, walls, etc. Symbols whose length can be scaled down and whose width cannot be scaled up are called semi-scaled symbols.

2) Geomorphological symbols generally represent landforms on topographic maps by contour lines. There are also some special landform symbols, such as ravines, terraces and cliffs. ) the terrain is small, the ground inclination is below, and the specific height is not more than 20m, which is called flat land;

The ground height changes greatly, and the dip angle is within 150m, which is called hilly land.

If the height changes greatly, the inclination angle is 0, and the specific height is above 150m, it is called a mountainous area;

The vast majority of slope angles exceed, which is called alpine land.

The main method of representing landforms on topographic maps is contour lines.

Isoenzyme

Definition of contour line

Contours are closed curves connected by adjacent points with equal elevation on the ground.

Vertical spacing and horizontal distance of contour lines?

The height difference between adjacent contour lines on the topographic map is called vertical spacing, which is expressed by, and is 10m in this drawing. The vertical spacing of the same topographic map is the same, so the vertical spacing of the topographic map is also called basic vertical spacing. The basic vertical intervals commonly used in large-scale topographic maps are 0.5m, 1m, 2m and 5m. The smaller the vertical interval, the more detailed the landform details expressed by contour lines.

The greater the vertical spacing, the rougher the detailed description of the landform. But when the vertical spacing is too small, the contour lines on the map are too dense, which will affect the clarity of the map. When surveying and mapping topographic maps, the appropriate basic vertical spacing should be selected according to the surveying and mapping scale, the ground slope of the survey area and the requirements of national specifications. The horizontal distance between adjacent contour lines is called contour distance, which is expressed by D. On the same topographic map, the smaller the horizontal distance of contour lines, the greater the slope, and vice versa. Therefore, we can judge the slope according to the density of contour lines on the map.

The framing and numbering of large-scale topographic map "1:5001:kloc-0/0001:2000 topographic map schema" stipulates that topographic map with scale of 1:500~ 1:2000. According to the need, other specifications of framing can also be adopted; Topographic map numbering generally adopts the coordinate kilometer numbering method of the southwest corner of the map section, and can also choose the running water numbering method or the row and column numbering method. When the kilometers in the southwest corner of the map are used, the X coordinate is in front and the Y coordinate is behind. The topographic map of 1:500 is 0.0 1km (such as 10.40-2 1.75), 1: 1000 and 65438. Strip survey areas or small survey areas can be numbered according to the unified sequence of survey areas, generally from left to right and from top to bottom with numbers 1, 2, 3, 4, ... (flow numbering method): the code (such as A, B, C, D ...) is generally taken as the horizontal line in the line numbering method, and the number is 65438 from top to bottom. (When the national unified coordinate system is adopted, the number of kilometers between drawings shall be marked with the number of belt and the number of hundred kilometers as required, such as X: 4327.8 and Y: 37457.0. )

4. After the control survey of large-scale topographic map is completed, put the theodolite (station) on the control point of the map root, measure the plane position and elevation of the surrounding features and geomorphological feature points (breakpoints), and make a map according to the scale. First, the exhibition control points

Use a drawing pencil or plotter to draw the root point of the drawing on white paper or polyester film with coordinate grid. After the control point is expanded, the side length obtained by the inverse calculation of two-point coordinates is used to check the points of the expanded point.

Second, the principle of large-scale topographic mapping

The topographic map is mapped by polar coordinate method, theodolite is placed at the station, and the horizontal angle α from the orientation direction to the inflection point is measured. Measure the distance d and height difference h from the station to the breakpoint by the method of sight distance measurement. Get the direction of the fracture point from α, and draw the fracture point on the diagram according to the distance d in this direction (except the denominator of the ruler). Add the height difference H to the station elevation to get the breakpoint elevation H, and mark the elevation of important breakpoints on the map.

Mapping of ground features: measure the feature points of ground features, and connect related breakpoints according to the ground feature symbols specified on the map.

Geomorphological mapping: measure geomorphological feature points and draw geological lines while measuring; According to the topographic points, contour interpolation is carried out according to the principle that contour is proportional to height difference.