Whereas most of the time it is assumed that the individual strata of sedimentary sequences are laterally continuous and of constant thickness, unconformities in the terrain can transform the boundaries of individual layers to for example conformable curves. Three basic type of conformities are starting off this chapter. the regional change in the thickness of undeformed, subhorizontal layers can be documented in isopachs. However, if the sedimentary beds are not horizontal, the vertical thickness may be larger than the true thickness. In such case the contours of equal vertical thickness are related to as isochores. The terms isopachs and isochores are described in the final two paragraphs of this chapter.