Modified Transverse Mercator

Producer Field Guide

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Producer Field Guide
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In 1972, the USGS devised a projection specifically for the revision of a 1954 map of Alaska which, like its predecessors, was based on the Polyconic projection. This projection was drawn to a scale of 1:2,000,000 and published at 1:2,500,000 (map E) and 1:1,584,000 (map B). Graphically prepared by adapting coordinates for the UTM projection, it is identified as the Modified Transverse Mercator projection. It resembles the Transverse Mercator in a very limited manner and cannot be considered a cylindrical projection. It resembles the Equidistant Conic projection for the ellipsoid in actual construction. The projection was also used in 1974 for a base map of the Aleutian-Bering Sea Region published at 1:2,500,000 scale.

Construction

Cone

Property

Equidistant

Meridians

On pre-1973 editions of the Alaska Map E, meridians are curved concave toward the center of the projection. On post-1973 editions, the meridians are straight.

Parallels

Parallels are arcs concave to the pole.

Graticule spacing

Meridian spacing is approximately equal and decreases toward the pole. Parallels are approximately equally spaced. The graticule is symmetrical on post-1973 editions of the Alaska Map E.

Linear scale

Linear scale is more nearly correct along the meridians than along the parallels.

Uses

USGS’s Alaska Map E at the scale of 1:2,500,000. Bathymetric Maps Eastern Continental Margin U.S.A., published by the American Association of Petroleum Geologists, uses the straight meridians on its Modified Transverse Mercator and is more equivalent to the Equidistant Conic map projection.

It is found to be most closely equivalent to the Equidistant Conic for the Clarke 1866 ellipsoid, with the scale along the meridians reduced to 0.9992 of true scale, and the standard parallels at latitude 66.09° and 53.50°N.