A closed curve connecting points with the same altitude on land is a contour line, and each contour line has a corresponding altitude. We call the height difference between adjacent contour lines the vertical interval.
The contour lines are vertically projected on the horizontal plane and drawn on the map according to a certain proportion to obtain the contour topographic map.
Contour topographic map can represent the ups and downs of a region, the trend and shape of mountains.
The contour line is closed, and the elevation rises from the outside to the inside, which is the top of the mountain.
The contour line is closed, and the elevation decreases from the outside to the inside, which is the basin topography;
Between the two peaks, the altitude is relatively high, and the two contour lines are relatively protruding, which is called saddle;
Where several contour lines overlap is a cliff.
Several contour lines are parallel and all protrude to low altitude. This is the ridge.
Several contour lines protrude to a higher altitude, so this is a valley.
Dense contour lines are steep slopes; The contour line is sparse, which is a gentle slope.
By layering and coloring the contour topographic map according to the altitude, you can get a layered and colored topographic map, which looks more vivid. You can directly observe the color to judge the terrain.
The famous Xin 'anjiang Reservoir, observing the edge of the island in the middle of the lake, the exposed loess looks like a contour line drawn on the lake from a height.
The construction of the reservoir flooded the low-lying land and the mountain peak became an island, hence the name Qiandao Lake. Qiandao lake water can meet the drinking water standard without any treatment, and is known as "the best water in the world"