How to survey the topographic map of mountainous areas

People see that the topographic map reflecting the shape and appearance of the earth's surface is quite complicated. Whether it is a mountainous area with undulating terrain or a level plain with dense rivers, lakes, ponds and water networks, various landforms and characteristic symbols on the map accurately reflect the actual situation on the ground. How are they mapped?

First of all, we must clearly determine the three basic elements needed for each point on the topographic map: orientation, distance and elevation. At the same time, these three basic elements must also be based on the starting direction, coordinate origin and elevation zero.

When surveying and mapping topographic map with a piece of white paper fixed on the drawing board, the drawing board should be oriented first, which can be oriented according to the geodetic control points measured in advance as the starting direction; In simple drawing, compass can also be used for orientation. After the drawing board is oriented, it is necessary to determine the position of the drawing point on the map, and there are unified and standardized coordinate points to be included in the national unified basic topographic map for surveying and mapping; But for small-area surveying and mapping, we can assume the independent origin of the plane rectangular coordinate system, and then we can begin to measure the plane coordinate position of any other point on the ground by measuring the azimuth and distance. As for the elevation of points, height system has laid out many leveling points with uniform elevation datum for use throughout the country, and generally, it can continuously measure the mapping area by leveling. Therefore, the point and elevation of any point can be determined at the same time by using the method of trigonometric leveling in surveying and mapping.

We know that any description of landforms and features on the ground can be reflected by lines composed of their transformation points. Geomorphology can reflect its height and morphological changes through contour lines; Features of houses, roads and rivers. Can be represented by lines formed by their transformation feature points; There are many special landforms and features and special legend symbols to represent them. Therefore, the work of mapping topographic map is actually to measure and represent the characteristic points of all landforms and features on the ground. Of course, topographic maps of different scales also have a problem of feature point selection and comprehensive complexity.

With the development and progress of surveying and mapping science and technology, a lot of heavy surveying and mapping work of modern topographic maps has also changed from traditional field white paper mapping to indoor aerial photography mapping and space remote sensing mapping, and gradually moved towards full digital and automatic mapping.