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MichaelOssipoff
(Stranger )
03/10/14 12:52 PM
 Re: Map projections [re: fmoretzsohn]

In regards to the post about an equal-area map for the Indo-Pacific region, why not use an obliqe local Aitoff-Hammer map?

Aitoff-Hammer is a projection for mapping the entire Earth, but it could also be used for any oblong-shaped smaller region, such as the Indo-Pacific region.

Aitoff-Hammer has a relatively symmetrical distortion-pattern. It's made by laterally expanding the Lambert Azimutha Equal Area projection.

An oblique Aitoff-Hammer would seem the most distortion-minimizing way to map the oblong-shaped region you spoke of.

Aitoff-Hammer is often just called "Hammer", and I'll so call it here henceforth, for brevity.

How Hammer is constructed:

Start with an oblique Lambert Azimuthal Equal Area projection. Say it's in equatorial aspect. Expand the map in the east-west dimension, by any factor, F, that you choose. In other words, multiply all east-west distances by F.

Now, re-label the meridians so that their labeling will be in keeping with the new east-west extent of the map. In other words, if F is 2, and you've doubled all of the east-west distances, then also double all of the longitude values of the meridians.

When Hammer is used as a world map, you start with a Lambert Azimuthal Equal Area map of half of the world, in equatorial aspect. The F value used is 2. That gives a 2:1 elliptical map of the world.

But:

1. The map needn't be in equatorial aspect. Of course it could be centered on any place in the world, in any orientation.

2. The map needn't be a map of the whole world. The above-described process for making Hammer from Lambert Azimuthal Equa Area could be used for any size region as well. And, of course F needn't be 2. It could be whatever value fits the shape of the region you want to map.

I haven't heard of Hammer being used for mapping a region smaller than the entire Earth, but it could be so used, as described above.

Hammer was introduced in 1892, based on an idea introduced by Aitoff 3 years previous. (Aitoff applied the east-west expansion to the Azimuthal Equidistant Projection).

Michael Ossipoff

 Entire thread Subject Posted by Posted on Map projections fmoretzsohn 03/09/04 02:08 PM Re: Map projections MichaelOssipoff 03/11/14 03:37 AM Re: Map projections MichaelOssipoff 03/10/14 01:53 PM Re: Map projections MichaelOssipoff 03/10/14 12:52 PM Re: Map projections scrabblehack 05/31/06 07:49 AM
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