To do this, the other properties-shape, angle, and scale-are distorted.

Equal area projectionsĮqual area projections preserve the area of displayed features. No map projection can preserve shapes of larger regions. The drawback is that the area enclosed by a series of arcs may be greatly distorted in the process. A map projection accomplishes this by maintaining all angles. To preserve individual angles describing the spatial relationships, a Conformal projection must show the perpendicular graticule lines intersecting at 90-degree angles on the map. Conformal projectionsĬonformal projections preserve local shape. Map projections designed for small-scale data are usually based on spherical rather than spheroidal geographic coordinate systems. One map projection might be used for large-scale data in a limited area, while another is used for a small-scale map of the world. Map projections are designed for specific purposes. The following diagram shows how three-dimensional features are compressed to fit onto a flat surface. In the graphic below, data near the poles is stretched.

A projection could maintain the area of a feature but alter its shape. Some projections are designed to minimize the distortion of one or two of the data's characteristics. Representing the earth's surface in two dimensions causes distortion in the shape, area, distance, or direction of the data.Ī map projection uses mathematical formulas to relate spherical coordinates on the globe to flat, planar coordinates.ĭifferent projections cause different types of distortions. The map projection has distorted the graticule.Ī spheroid can't be flattened to a plane any more easily than a piece of orange peel can be flattened-it will rip. The shape of the graticule on the flat paper is different from that on the earth. You can now unwrap the paper and lay it flat. A light at the center of the earth will cast the shadows of the graticule onto the piece of paper. Imagine the earth's surface is clear with the graticule drawn on it. One easy way to understand how map projections alter spatial properties is to visualize shining a light through the earth onto a surface, called the projection surface. This mathematical transformation is commonly referred to as a map projection. Whether you treat the earth as a sphere or a spheroid, you must transform its three-dimensional surface to create a flat map sheet.

Flat earth map projection