The outline shapes and general appearances of world maps are chosen to meet design requirements, improve feature displays, or create novel designs. To the map user the outline shape of a map is significant for several reasons. First and foremost, the shape of the frame often affects the internal properties of the map projection and thus the patterns of scale variation and distortion. The frame is also an edge along which the continuous surface of the earth is interrupted.
Shapes of maps vary from simple to complex. Most conventional projections have simple, compact, and familiar outer boundaries such as circles, ovals, and rectangles. Circular and oval outlines evoke the fundamental roundness of the earth. The rectangle, with its square corners, is unrelated to the smooth roundness of a sphere but is often seen, perhaps because its shape fits nicely in the common format of a printed page or poster. The focus of this chapter is on less familiar outlines.
Among the less conventional forms are perspective-like world map projections introduced by Raisz in 1943. One, his Armadillo projection, frequently used on reference and distribution maps (Figure 3-1), resembles that mammal when curled up for protection. That the scale decreases away from the center is evident from the graticule, and this concept is reinforced by the curled shape of the external frame.
The discontinuities of such features as continents or oceans that result from the use of a frame bounded by meridians and parallels have led to a variety of enhancements. The simplest is to extend the map on both sides beyond its 360° width to an extent that avoids feature discontinuity through feature repetition. Minor marginal extensions to preserve continuity of continental edges are common.
A succession of views, each relatively undistorted, can be portrayed with interrupted projections as described in Chapter 2. The more interruptions, the more complex the frame.
The diverse and ingenious world maps of this group result from the eternal struggle to comprehend and communicate spherical concepts via plane representations.
Continental Distributions. The optimum "land hemisphere" (see Figure 4-3A), centered in France, excludes southern South America, Antarctica, New Zealand, Australia, and southern Asia. This creates major problems in fully representing the continents since scale variations and distortions increase markedly as coverage extends into the second hemisphere. One approach was introduced by Frye in 1895 to illustrate land-based features with the Atlantic and Arctic basins on one side and much of the Pacific Ocean omitted (Figure 3-2).
Oceanic Distribution. The vast extent and complex outline of the oceans present an especially challenging representation task. As with continental distributions, this task also has led to the use of interrupted projections. One of Spilhaus's maps of the world ocean is an interrupted (nearly) equal-area arrangement (Figure 3-3), which he says resembles a "crazy tulip". Preserving ocean continuity adds to the difficulty. This problem has been addressed recently with three lobes based on transverse Hammer equal-area projections by Spilhaus and Snyder (Figure 3-4). This arrangement is centered at the South Pole and uses shorelines to replace the curved graticule-like lines normally bounding the projection.
Tectonic Plate Distributions. Spilhaus contributed numerous maps in a study of tectonic or crustal plate arrangements, some including polyhedral arrangements. On an interrupted transverse Sinusoidal equal-area arrangement with four lobes, the seven major tectonic plates were mapped in a way that allowed comparison of plate areas and preserved plate shapes reasonably well (Figure 3-5). Spilhaus also mapped the major plates on the seven faces of an irregular polyhedron.
Artistic Views. In addition to their informational function, the varied shapes of world map projections have led to their use as emblems on atlas and book covers, on letterheads, and in advertising. Selected examples are provided in Figure 3-6.
Missing and False Frames
The important relationship of the shape of the frame to the internal design of a map projection, mentioned earlier, is especially significant for interrupted projections. Misleading maps can result when the map frame and graticule are omitted from a map projection interrupted in the oceans. This is sometimes done for design reasons, but on black-and-white maps oceanic areas and the non-map background are indistinguishable. This misleading effect is visually enhanced on multicolored maps where the blue "ocean" extends over non-map areas.
On some maps the actual outline of a world map has been replaced by an arbitrary enclosing line, which can be called a false frame because it is intended to create a different visual impression from the one provided by the true frame. This technique is sometimes used in advertising literature. One finds oval outlines enclosing areas mapped on a rectangular projection, and vice versa.
Numerous modifications and combinations of standard projections have resulted in the creation of world maps with a wide variety of shapes. They may seem eccentric, but the group represents serious efforts to improve the portrayal of particular concepts or distributions. Attention to the shapes of these maps is important because they affect the internal properties of projections, internal grid discontinuities, and the spherical concepts and patterns being represented.
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