The manual of computer-based methods currently employed in exploration to produce structure-contour maps of coal seams requires numerous drill holes to provide the necessary three-dimensional control. The following method, illustrated by maps of coal seams from the Rocky Mountain foothills of Alberta, uses only orientational, stratigraphic, and positional data from outcrops. It has four steps: (1) establishment of structural domains within which the coal is approximately cylindrically folded; (2) construction of the coal seam's profile in each domain; (3) projection of each profile parallel with its fold axis in order to generate the coordinates of a set of points on the seam in each domain; (4) computer contouring of the resulting elevations. The first and fourth steps u e known procedures. The second step can be carried out graphically using a computer plot showing the geographic location, stratigraphic position, and bedding trace of each outcrop projected onto a plane normal to the fold axis. Alternatively, where the stratigraphic positions of the outcrops are known precisely enough and the structure is not too complex, the computer can be instructed to interpolate the coal seam between the various projected outcrops. The third step involves using the appropriate digitized profile and fold axis to predict the coal seam's depth beneath each outcrop and saving these values for the contouring stage.

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