Quartic Authalic

Producer Field Guide

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Producer Field Guide
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Meridians are fourth-order (quartic) curves. Outer meridians at high latitudes have great distortion. If Quartic Authalic projection is interrupted, distortion can be reduced.

Construction

Pseudocylindrical

Property

Equal-area

Meridians

Central meridian is a straight line, and is 0.45 as long as the Equator. The other meridians are curves that are equally spaced. They fit a "fourth-order (quartic) equation and concave toward the central meridian" (Snyder and Voxland, 1989).

Parallels

Parallels are straight parallel lines that are unequally spaced. The parallels have the greatest distance between in proximity to the Equator. Parallel spacing changes slowly, and parallels are perpendicular to the central meridian.

Graticule spacing

See Meridians and Parallels. Poles are points. Symmetry exists about the central meridian or Equator.

Linear scale

Scale is accurate along the Equator. Scale is constant along each latitude, and is the same for the latitude of opposite sign.

Uses

World maps.

McBryde-Thomas Flat-Polar Quartic projection uses Quartic Authalic as its base (Snyder and Voxland, 1989).

Source: Snyder and Voxland, 1989

Quartic Authalic Projection

map_projection_quartic_authalic

Source: Snyder and Voxland, 1989