Albers Equal-Area Conic Projection

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Introduction

The Albers Equal-Area Conic Projection is an area-preserving conic projection widely used in geographic information systems (GIS) and cartography.

The projection is created by wrapping the Earth’s surface in a cone and unrolling it. It is based on two standard parallels (usually set in mid-latitudes) between which the shape of the area is minimally distorted while preserving the true area.

This projection is widely used for mapping the United States, but is also suitable for countries or regions located in mid-latitudes such as Japan.

This projection is different from a formal geodetic projection and is not usually provided as a standard feature in general-purpose cartography or GIS tools. However, it is often used in visual analysis, education, or visualizations to show the relationship between specific areas.

Projection Basics

In geospatial data formats such as GeoTIFF, Shapefile, GeoJSON, etc., the parameters of the Albers Equal Area Conic projection include:

1. Projection mode: Albers_Equal_Area
2. Standard Parallel 1 (Standard_Parallel_1)
3. Standard Parallel 2 (Standard_Parallel_2)
4. Latitude of Origin (Latitude_Of_Origin)
5. Central Meridian (Central_Meridian)
6. False Easting (False_Easting)
7. False Northing (False_Northing)
8. Datum (such as NAD83, GRS80, etc.)
9. Unit (for example: Meter)

Pros

1. The area remains accurate, suitable for calculating the area of forests, farmlands, waters, etc.
2. The shape distortion is small near the standard latitude
3. Good display balance can be achieved in the mid-latitude area (about 30 to 50 degrees)
4. Suitable for the production of distribution maps of climate, environment, soil, etc.

Cons

1. Although the area is accurate, the shape, distance, and direction are easily distorted
2. The accuracy will be reduced in high-latitude or low-latitude areas
3. Not suitable for global map representation (more suitable for local areas)

Application Scenario

The Albers Conic projection is particularly suitable for statistical or thematic map production that requires area accuracy, such as forest resource management, soil classification, land cover classification, population density, climate zone visualization, etc., especially in situations where area distribution information is important.

In addition, in countries with a large east-west span such as the United States and Canada, it is often used as a national standard projection method.

Example

1. The Albers equal-area conic projection has standard parallels set at 20 degrees north and 50 degrees north.

2. Albers equal-area conic projection with standard parallels set at 15 and 45 North and Tissot’s indicator ellipse.

Related GIS Projections

Mercator Projection

Transverse Mercator Projection

Wagner Projection

Longitude / Latitude Projection

References

1. https://pro.arcgis.com/en/pro-app/latest/help/mapping/properties/albers.htm#:~:text=Sources-,Description,west%20orientation%20at%20mid%2Dlatitudes.
2. https://en.wikipedia.org/wiki/Albers_projection
3. https://support.esri.com/en-us/gis-dictionary/albers-equal-area-conic-projection