Orthographic

Producer Field Guide

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Producer Field Guide
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The Orthographic projection is geometrically based on a plane tangent to the Earth, and the point of projection is at infinity. The Earth appears as it would from outer space. Light rays that cast the projection are parallel and intersect the tangent plane at right angles. This projection is a truly graphic representation of the Earth, and is a projection in which distortion becomes a visual aid. It is the most familiar of the azimuthal map projections. Directions from the center of the projection are true.

Construction

Plane

Property

Compromise

Meridians

Polar aspect: the meridians are straight lines radiating from the point of tangency.

Oblique aspect: the meridians are ellipses, concave toward the center of the projection.

Equatorial aspect: the meridians are ellipses concave toward the straight central meridian.

Parallels

Polar aspect: the parallels are concentric circles.

Oblique aspect: the parallels are ellipses concave toward the poles.

Equatorial aspect: the parallels are straight and parallel.

Graticule spacing

Polar aspect: meridian spacing is equal and increases, and the parallel decreases from the point of tangency.

Oblique and equatorial aspects: the graticule spacing decreases away from the center of the projection.

Linear scale

Scale is true on the parallels in the polar aspect and on all circles centered at the pole of the projection in all aspects. Scale decreases along lines radiating from the center of the projection.

Uses

National Atlas by USGS.

This projection is limited to one hemisphere and shrinks those areas toward the periphery. In the polar aspect, latitude ring intervals decrease from the center outwards at a much greater rate than with Lambert Azimuthal. In the equatorial aspect, the central meridian and parallels are straight, with spaces closing up toward the outer edge.

The Orthographic projection seldom appears in atlases. Its utility is more pictorial than technical. Orthographic has been used as a basis for maps by Rand McNally and the USGS.

Three views of the Orthographic projection are shown in the figure below:

A) Polar aspect

B) Equatorial aspect

C) Oblique aspect, centered at 40°N and showing the classic globe-like view.

Orthographic Projection

map_projection_orthographic