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## 5.4.7 General Cylindrical Projections (-Jy -JY)

This cylindrical projection is actually several projections, depending on what latitude is selected as the standard parallel. However, they are all equal area and hence non-conformal. All meridians and parallels are straight lines. The requirements to define this projection are:

  The central meridian

  The standard parallel

  Scale in inch/degree or as 1:xxxxx (-Jy), or map width (-JY)

While you may choose any value for the standard parallel and obtain your own personal projection, there are four choices of standard parallels that result in known (or named) projections. These are listed in Table 5.1.

Table 5.1: Standard parallels for some cylindrical projections.
Projection name | Standard parallel
Lambert | 0
Behrman | 30
Trystan-Edwards | 3724' (= 37.4)
Peters (Gall) | 45

For instance, a world map centered on the 35E meridian using the Behrman projection can be obtained by running the command:

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

    pscoast -R-145/215/-90/90 -JY35/30/4.5i -B45g45 -Dc -A10000 -S200 -W0.25p -P > GMT_general_cyl.ps

Figure 5.24: World map using the Behrman cylindrical projection.

As one can see there is considerable distortion at high latitudes since the poles map into lines.

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