6.4.5 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:

pscoast -Rg -JKf180/4.5i -Bg30/g15 -Dc -A10000 -W0.25p -Gwhite -Slightgray -P > GMT_eckert4.ps

Figure 6.25: World map using the Eckert IV projection.

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

Figure 6.26: World map using the Eckert VI projection.