Sand and shale thickness and position (depth) rasters were calculated by extrapolating from sand thickness and depth to top and bottom of formation, which were obtained from various sources in the form of scanned isoline maps. The relevant isolines were digitized and the values extrapolated to create rasters of the areas of interest representing sand thickness, etc. at a 1km resolution. It was assumed that shale accounted for all material within each formation that did not consist of sand, and that all of the shale occurred equally above and below the midpoint depth of the formation for any given location. Rasters representing shale thickness and midpoint depth were calculated using simple math (addition, subtraction, etc.) on the sand thickness and formation depth rasters.
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