In order to illustrate a 3D structure of an area, a map in general is not enough. Therefore, cross-sections of the area may accompany the map. The construction of cross-sections across any geological structure involves the risk of several geometric distortions. This chapter outlines the nature of these distortions. The first paragraph provides guidelines for selecting section lines that show the most appropriate view of the subsurface. Secondly further instructions for profile construction are given. The third paragraph deals with visual distortions occuring in differentially scaled cross-sections. The effects of apparent thickness and dip, discussed in the previous chapter, are resumed in section 4-4.