− | A contour map of equal values of true stratigraphic thickness is an ''isopach map'' ([[:file:subsurface-maps_fig4.png|Figure 4]]). Except for vertical wells in horizontal beds, corrections for wellbore deviation and formation dip are needed to make isopach maps. | + | A contour map of equal values of true stratigraphic thickness is an ''isopach map'' ([[:file:subsurface-maps_fig4.png|Figure 4]]). Except for vertical wells in horizontal beds, corrections for [[Wellbore trajectory|wellbore deviation]] and formation [[dip]] are needed to make isopach maps. |