Description
The Albers projection is an equal area conic projection. It uses two standard parallels to reduce some of the distortion found in a projection with only one standard parallel. The projection is best suited for land masses extending in an east-to-west orientation at mid-latitudes. It is often used for maps of the contiguous United States, Europe, and Australia.
The Albers projection was introduced by Heinrich C. Albers in 1805. Ellipsoidal equations were developed by Oscar S. Adams in 1927. It is available in ArcGIS Pro 1.0 and later and in ArcGIS Desktop 8.0 and later.
Projection properties
The subsections below describe the Albers projection properties.
Graticule
Albers is a conic projection. All meridians are equally spaced straight lines converging to a common point. The parallels and both poles are represented as circular arcs centered on the point of convergence of the meridians. The spacing of the parallels decreases toward the poles. When the standard parallels are set on the northern hemisphere, the fan-shape of the graticule is oriented up (see the image on the left, above). When the standard parallels are on the southern hemisphere, the fan-shape of the graticule is oriented down (see the image on the right, above). The graticule is symmetric across the central meridian.
Distortion
Albers is an equal-area (equivalent) projection. Shapes, directions, angles, and distances are generally distorted. The scale, directions, and distances are true only along the standard parallels. Distortion values grow away from the standard parallels. Distortion values are the same along any given parallel and symmetric across the central meridian.
Usage
This projection is best suited for equal-area mapping of land masses in mid-latitudes extending in an east-to-west orientation rather than those extending north to south. It is best practice to place standard parallels at one-sixth of the latitude range below the top and above the bottom of the area to be mapped. After ellipsoidal equations were developed, the projection became standard for equal-area maps of the United States.
Limitations
The standard parallels can be at any latitude, except set at opposite poles.
Parameters
Albers parameters are as follows:
- False Easting
- False Northing
- Central Meridian
- Standard Parallel 1
- Standard Parallel 2
- Latitude Of Origin
Particular parameter cases
If both standard parallels are set to a pole, the resulting projection is the Lambert azimuthal equal-area projection in polar aspect. When one of the standard parallels is set at a pole, the outcome is the Lambert equal-area conic projection. The cylindrical equal-area projection can be obtained only by setting standard parallels symmetrically north and south of the equator.
Sources
Snyder, J. P. (1987). Map Projections: A Working Manual. U.S. Geological Survey Professional Paper 1395. Washington, DC: United States Government Printing Office.
Snyder, J. P. (1993). Flattening the Earth. Two Thousand Years of Map Projections. Chicago and London: University of Chicago Press.
Snyder, J. P. and Voxland, P. M. (1989). An Album of Map Projections. U.S. Geological Survey Professional Paper 1453. Washington, DC: United States Government Printing Office.