[Comment on] Projection ponderings

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Abstract

I read with interest the article on world projections by F. Webster McBryde (Eos, Dec. 1, 1981, p. 1162). The need for some sort of equal area world map is obvious, and there are many choices available for projections and how to split the different ocean basins. Below are examples of a special mollweide Equal Area Elliptic map that I have found to be convenient for displaying world oceanic data.

There are many useful features of the map: (1) Many deep and bottom water characteristics of the world ocean originate in the north and south Atlantic and are carried eastward in the circumpolar current to the other ocean basins. Thus the Atlantic Ocean should be on the left with the other two oceans placed to the east. (2) Each ocean has the same central longitude for the northern and southern hemispheres, minimizing N-S distortions within oceans. Each ocean can be used separately without the strange looking N-S longitude skews that appear in McBryde's Atlantic and Indian ocean maps and also in all three oceans in the familiar University of Chicago Goode base map used by Sverdrup, Fleming, and Johnson (1942). Work begun in a single ocean area can be expanded easily to the other oceans without redoing the original data set (an exercise I went through when switching from a map made on a Pacific Ocean Lambert equal area chart to a world-wide map). (3) The Atlantic-Indian ocean split places the Mediterranean with the Atlantic Ocean and the Red Sea with the Indian Ocean. (4) Latitude lines are straight for easy ocean to ocean comparison. (5) Equations for the mollweide projection are readily available for computer mapping programs, facilitating computer generated oceanographic data fields for contouring. My maps are usually computer plotted 40 inches high for each ocean, contoured, and then reduced by 50% for drafting.

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