1. A method for automatically determining contours of heights of a relief, of a geographical area (ZO), the method comprising: a) on the basis of an image of said geographical area (ZO), which contains altimetric data of points therein, a background surface of the relief which illustrates gradual variations in altitudes of said geographical area (ZO) is eliminated, by implementing a top hat algorithm, which uses a structuring element ( 28 ) which is adjustable; b) on the basis of step a), thresholding is performed on the image of said geographical area (ZO) to form a binary image (IB) of the relief seen from above, containing only reliefs having heights above a threshold value which is adjustable, wherein the threshold value is calculated using a noise tolerance parameter wherein T=k−σ, wherein k is a coefficient of standard deviation and a is the standard deviation of altitudes in the altimetric data; c) from this binary image (IB) which comprises two different types (Z 1 , Z 2 ) of area, rough contours of the heights of the relief are extracted, illustrating the boundaries between these two different types (Z 1 , Z 2 ) of area; and d) said rough contours are simplified so as to obtain a set of polygons (P 1 , P 2 , P 3 ) illustrating the contours (C 1 , C 2 , C 3 ) of the heights of the relief of said geographical area (Z 0 ).