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 $\pm$ 40$^{o}$30' (IV) and $\pm$ 49$^{o}$16'’ (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

$\bullet$

The central meridian

$\bullet$

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