The second language of geography is a cartographic image. Maps were used even by ancient sailors. When planning the expedition, researchers collected all available cartographic materials for the required area. Upon completion, the results were transferred to paper. Thus a terrain plan was created. This was the basis for creating new maps. What is a terrain plan and what are its fundamental differences from a geographical map?
What is a terrain plan ?
The very first maps in human history were plans. Now they are used in almost all branches of science and technology: they can not do without them in construction, agriculture, engineering surveys, etc.
A terrain plan is a large-scale image of a plot of the earth’s surface that uses conventional signs to create it. As a rule, cartographic images are compiled for small areas with areas up to several square kilometers. In this case, the curvature of the earth's surface does not affect the image.
How is the plan different from the map?
Often in life we come across both a map and a plan of the area. Geography as a science is based on these cartographic images. But this is not the same thing.
When creating a geographical map, a smaller scale is used (that is, a larger area is covered), the nature of the earth's surface is taken into account, that is, the mathematical law of image construction - projection is used. The most important element of geographical maps is the degree grid: it is necessary to determine the cardinal points. Parallels and meridians are often displayed as arcs rather than straight. Only significant large objects are subject to mapping. A variety of materials are used to compile them, including maps of a larger scale, and satellite images.
A terrain plan is a more detailed image of a small piece of the Earth. It is built without taking into account the projection, since, due to the size of the plot, the surface is considered to be flat. The cardinal points are determined by the directions of the plan framework. All elements of the terrain are subject to display. Compose them on the basis of large-scale aerial photographs or on the ground.
How is the plan drawn up?
To begin with, a point is selected on the site from which the entire area to be mapped is clearly visible. After that, you need to choose the scale of the future plan. The next step is to determine the direction to the north. This can be done using a tablet-board and a hand compass. On paper, you need to identify the point from which the terrain will be surveyed, and then draw all the main landmarks (building corners, large trees, poles).
Then, using special high-precision instruments, azimuths are measured to each point that needs to be reflected on the plan. Each time, azimuths are laid off from the main point, and an auxiliary line is drawn from it, an angle is marked on the plan. The distance from the main to the desired points of the terrain is also measured and transferred to paper.
Then, in the conventional signs, the objects of the site are displayed, the necessary signatures are made.
Scale of the terrain plan
Over the entire area of the cartographic image of the plan, its scale remains unchanged. The scale is of three types:
The number is expressed as a fraction, the numerator of which is 1, and the denominator is M. This number M shows the degree of reduction in image size on the plan. Topographic plans have the scales 1: 500, 1: 1000, 1: 2000, 1: 5000. For land management works, smaller scales of plans are also used - 1:10 000, 1:25 000, 1:50 000. The scale with the larger number M is considered smaller, and vice versa.
Named scale is simpler - here the length of the lines is expressed verbally. For example, 1 cm - 50 meters. This means that 1 cm of distance on the plan corresponds to 50 m on the ground.
A linear type scale is a graph depicted as a straight line segment that is divided into equal parts. Each such part is signed by a numerical value of the proportional length of the terrain.
Conditional signs of the plan of the district
In order to display any objects or processes on the topographic plan, to indicate their important qualitative or quantitative values, it is necessary to use conventional signs or symbols. They give a complete picture of the spatial arrangement of objects, as well as their characteristics and appearance.
There are four types of symbols:
- Large-scale - linear and areal (for example, state squares, roads, bridges).
- Scale-free (well, spring, pillar, tower, etc.).
- Explanatory (signatures of characteristics of objects, for example, highway width, names of entities).
In the legend of the plan, they are all reflected. Based on the legend, a primary idea of the site is compiled.
So, the terrain plan is a cartographic image of a small plot of the earth's surface on a large scale. It is used in almost all areas of human activity. Without it, it would be impossible to create topographic maps.