The precision of contour lines and contour intervals of large- and medium-scale maps

Abstract

A study is conducted to derive estimates for the precision of contour lines and contour intervals on technical and topographical maps at scales ranging from 1:250 to 1:50000, where the topography is assumed to be surveyed by photogrammetric methods only. Slopes are assumed ranging from 4° to 45°. The concept of a tubular confidence space of a contour line is introduced. It is possible to express the variances of the position of spot heights and contour lines—as well as the variances of their relative horizontal and vertical positions—as relatively simple functions of the focal distance f of the camera lens, the scale of the photograph S N and the scale of the map, thereby separating the parameters pertaining to the photogrammetric procedures from those of the actual plotting. It is proposed to add these parameters f and S N as well as the scale of the manuscript to the legenda of the maps concerned, in order to have a better insight into the precision. Comparison is made with some existing formulae (see section “Final remarks”). Estimates are also given for the precision of heights, slopes and slope distances as derived from horizontal measurements in the map. Subsequent studies with respect to the precision of morphometric measurements of areas, volumes, slope analysis, etc. are in an advanced stage, and it is hoped that they can be published in the near future. Important formulae are 64–67 and 72–74.