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## 5.5.5 Eckert IV and VI Projection (-Jk -JK)

The Eckert IV and VI projections, presented by Max Eckert in 1906, are pseudocylindrical equal-area projections. Central meridian and all parallels are straight lines; other meridians are equally spaced elliptical arcs (IV) or sinusoids (VI). The scale is true along latitudes 4030' (IV) and 4916' (VI). Their main use is in thematic world maps. To select Eckert IV you must use -JKf (f for ``four'') while Eckert VI is selected with -JKs (s for ``six''). If no modifier is given it defaults to Eckert VI. In addition, you must enter

  The central meridian

  Scale along equator in inch/degree or 1:xxxxx (-Jk), or map width (-JK)

Centered on the Dateline, the Eckert IV example below was created by this command:

    #!/bin/sh
    #    $Id: GMT_eckert4.sh,v 1.1 2001/03/21 04:10:21 pwessel Exp $
    #

    pscoast -R0/360/-90/90 -JKf180/4.5i -Bg30/g15 -Dc -A10000 -W0.25p -G255 -S200 -P > GMT_eckert4.ps

Figure 5.30: World map using the Eckert IV projection.

The same script, with s instead of f, yields the Eckert VI map:

Figure 5.31: World map using the Eckert VI projection.

Next: 5.5.6 Sinusoidal Projection (-Ji Up: 5.5 Miscellaneous Projections Previous: 5.5.4 Robinson Projection (-Jn Contents Index