Abstract: Inconsistencies in Resource-Appraisal Estimates Resulting from Areal Distortions Inherent in Some Map Projections

F. E. Lennartz, B. M. Miller

Accurate computation of sediment volumes in basins with petroleum potential is of primary concern in many resource-appraisal methods. Inaccurate measurement of areas may distort sediment-volume calculations significantly, and result ultimately in misleading resource estimates. The chief cause of inaccurate area measurement is the scale deviation within certain map projections, which results in a distortion of the total area measured. This scale deviation is inherent in many map projections that have been designed for purposes other than area measurements. Maps based on these projections, nevertheless, are used for areal measurement because equal-area maps of the sedimentary basins being assessed are not available. Transference of these data to an equal-area map projection is time-consuming and may be highly inaccurate, because it frequently involves estimating the positioning of certain boundaries. Areal distortions for a number of map projections showing Alaska and neighboring regions are treated in this study, because of the great interest in estimating the petroleum resources of Alaska and other Arctic areas. Map projections discussed include the Mercator, the transverse Mercator, the bipolar oblique conic conformal, the Albers equal area, and others. Some of the maps discussed are the U.S. Geological Survey Tectonic Map of North America, the American Geographical Society Map of the Arctic Region, a "Petromotion" map of eastern Alaska and western Canada, and the U.S. Geological Survey Map E of Alaska, 1954 and 1975 editions.

A method of calculating areal distortion is described. Ranges in sediment volumes for the basins studied are reported. For each of the volumetric estimates, the ranges are based on the distortion within the maps used for the study.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA