The Albers Equal-Area Conic projection uses two standard parallels to reduce some of the distortion produced when only one standard parallel is used. Although neither shape nor linear scale are truly correct, the distortion of these properties is minimized in the region between the standard parallels. This projection is best suited for landmasses that extend more in the east-to-west orientation than those lying north to south.
Method of Projection - Conic:
In this projection, the meridians are equally-spaced straight lines converging at a common point. Poles are represented as arcs rather than by single points. Parallels are unequally spaced concentric circles, whose spacing decreases toward the poles.
Properties:
Shape:
Shape along the standard parallels is accurate and minimally distorted in the region between the standard parallels and those regions just beyond. The 90-degree angles between meridians and parallels are preserved, but because the scale along the lines of longitude does not match the scale along lines of latitude, the final projection is not conformal.
Area:
All areas are proportional to the same areas on the Earth.
Direction:
Locally true along the standard parallels.
Distance:
Projection distances are best in the middle latitudes. Along parallels, scale is reduced between the standard parallels and increased beyond them. Along meridians, scale follows an opposite pattern.
Limitations:
Best results for regions predominantly east-west in extent and located in the middle latitudes. Total range in latitude from north to south should not exceed 30 - 35 degrees. No limitations on east to west range.
Uses and Applications:
Used for small regions or countries, but not for continents.
Conterminous United States, normally using 290 30' and 450 30' as the two standard parallels. For this projection, the maximum scale distortion for the 48 states is 1.25 percent.
Recommended choice of standard parallels can be calculated by determining the range in latitude from degrees north to south and dividing this range by six. Using the 'One-Sixth Rule' to determine standard parallels means that the 1st standard parallel is the southern boundary plus one-sixth the range and the 2nd standard parallel the northern limit minus one-sixth the range. There are also other possible approaches.
