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  • The Albers equal-area conic projection, or Albers projection, is a conic, equal area map projection that uses two standard parallels. Although scale and shape are not preserved, distortion is minimal between the standard parallels. It was first described by Heinrich Christian Albers (1773-1833) in a German geography and astronomy periodical in 1805.


    Official adoption


    The Albers projection is used by some big countries as "official standard projection" for Census and other applications.

    Some "official products" also adopted Albers projection, for example most of the maps in the National Atlas of the United States.


    Formulas




    = For Sphere

    =
    Snyder describes generating formulae for the projection, as well as the projection's characteristics. Coordinates from a spherical datum can be transformed into Albers equal-area conic projection coordinates with the following formulas, where




    R



    {\displaystyle {R}}

    is the radius,



    λ


    {\displaystyle \lambda }

    is the longitude,




    λ

    0




    {\displaystyle \lambda _{0}}

    the reference longitude,



    φ


    {\displaystyle \varphi }

    the latitude,




    φ

    0




    {\displaystyle \varphi _{0}}

    the reference latitude and




    φ

    1




    {\displaystyle \varphi _{1}}

    and




    φ

    2




    {\displaystyle \varphi _{2}}

    the standard parallels:








    x



    =
    ρ
    sin

    θ




    y



    =

    ρ

    0



    ρ
    cos

    θ






    {\displaystyle {\begin{aligned}x&=\rho \sin \theta \\y&=\rho _{0}-\rho \cos \theta \end{aligned}}}


    where








    n



    =



    1
    2




    (

    sin


    φ

    1


    +
    sin


    φ

    2



    )





    θ



    =
    n

    (

    λ


    λ

    0



    )





    C



    =

    cos

    2




    φ

    1


    +
    2
    n
    sin


    φ

    1






    ρ



    =



    R
    n





    C

    2
    n
    sin

    φ







    ρ

    0





    =



    R
    n





    C

    2
    n
    sin


    φ

    0










    {\displaystyle {\begin{aligned}n&={\tfrac {1}{2}}\left(\sin \varphi _{1}+\sin \varphi _{2}\right)\\\theta &=n\left(\lambda -\lambda _{0}\right)\\C&=\cos ^{2}\varphi _{1}+2n\sin \varphi _{1}\\\rho &={\tfrac {R}{n}}{\sqrt {C-2n\sin \varphi }}\\\rho _{0}&={\tfrac {R}{n}}{\sqrt {C-2n\sin \varphi _{0}}}\end{aligned}}}



    = Lambert equal-area conic

    =
    If just one of the two standard parallels of the Albers projection is placed on a pole, the result is the Lambert equal-area conic projection.


    See also


    List of map projections


    References




    External links



    Mathworld's page on the Albers projection
    Table of examples and properties of all common projections, from radicalcartography.net
    An interactive Java Applet to study the metric deformations of the Albers Projection.

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