Changes

A contour map of equal values of true stratigraphic thickness is an ''isopach map'' (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'' (Figure 4). Except for vertical wells in horizontal beds, corrections for wellbore deviation and formation dip are needed to make isopach maps.

[[file:subsurface-maps_fig4.png|thumb|{{figure number|4}}(a) Cross section and (b) net pay Isopach map of the Strachan gas field, western Canada. Contour Interval is [[length::100 ft]]. (From <ref name=pt06r55>Hriskevich, M. E., Faber, J. M., Langton, J. R., 1980, Strachan and Ricinus West gas fields, Alberta, Canada, in Halbouty, M. T., ed., Giant Oil and Gas Fields of the Decade 1968–1978: AAPG Memoir 30, p. 315–327.</ref>.)]]

[[file:subsurface-maps_fig4.png|thumb|{{figure number|4}}(a) Cross section and (b) net pay Isopach map of the Strachan gas field, western Canada. Contour Interval is 100 ft. (From <ref name=pt06r55>Hriskevich, M. E., Faber, J. M., Langton, J. R., 1980, Strachan and Ricinus West gas fields, Alberta, Canada, in Halbouty, M. T., ed., Giant Oil and Gas Fields of the Decade 1968–1978: AAPG Memoir 30, p. 315–327.</ref>.)]]

===Isochore===

===Isochore===