Understanding interpolation allows you to wisely choose the number and passion of the points to be surveyed.
The altitude at point M Located between the contour lines
530 and 540 is determined by considering the constantly sloping ground between A and B.
Points A and B are the closest points to M on contour lines 530 and 540; here ΔH = 10 m.
The slope at point M is : p = ΔH
ab
The distance ab is the real distance, that is to say the distance measured on the plan and divided by the scale of the plan.
The altitude of M is : HM = HA + am ΔH
ab
This last formula can be applied with the distances measured on the plan; the scale factor simplifies.
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