Map Projections: Classic Interrupted Maps

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Map Projections

Classic Interrupted Maps

Interrupted Mollweide Map

Interrupted Mollweide hemispheres, central meridians 110°W and 70°E

Due to their constant scale along each parallels, pseudocylindrical projections are especially appropriate for interruptions along meridians, with lobes beginning at the Equator. For instance, on an interrupted Mollweide map, area is still preserved, meridians are still mapped to elliptical arcs, and those at (after any oblique rotation) 90°W and 90°E are circular. Therefore, the simple form with symmetrical central meridians comprises two perfect circles. Compare the azimuthal orthographic and stereographic maps of exactly the same regions.

Interrupted Mollweide map, simplified arbitrary lobes

Circa 1916, before designing his most famous projection, John Paul Goode experimented interrupting pure sinusoidal and Mollweide maps. In an arrangement slightly more complex than that shown here, the result became popular but was eventually superseded by the true homolosine projection.

Interrupted Goode Homolosine Projection

Interrupted Goode homolosine map; Iceland and portions of Greenland and Eastern Asia appear twice.

This is a common form of J.P. Goode's homolosine projection, easily recognized due to its broken meridians. The lobe arrangement shown here is similar to that originally published by Goode (1923-1925). Some maps of this kind include extensions repeating a few portions in order to show Greenland and eastern Russia uninterrupted.

Interrupted Boggs Eumorphic

Interrupted eumorphic map with extensions repeating Greenland and the Behring sea region. The break in Eurasian meridians is clearly visible.

Boggs preferred his hybrid eumorphic projection in an interrupted form resembling Goode's homolosine maps. Since it averages the sinusoidal and Mollweide projections instead of joining bands projected separately, meridians in an eumorphic map are unbroken except (arbitrarily) at the Eurasian lobe: Boggs usually employed a different central meridian north of the 40°N parallel.

Approximate reconstruction of the Sinu-Mollweide projection in interrupted form

Interrupted Sinu-Mollweide Projection

Like Goode, Allen Philbrick preferred his Sinu-Mollweide projection in an interrupted format privileging lands. In contrast with the homolosine and other pseudocylindricals, Philbrick's interruptions do not cut from poles to the Equator, which creates additional direction breaks besides those along the fusion parallel. In the top half, the two lobes are split from the rotated pole up; in the bottom half, the three lobes are split starting from around the original 10°S parallel.

Philbrick's original maps have borders zigzagging along graticule lines; he also repeated portions of Alaska to keep it unsplit, and sometimes left out Antarctica.

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