Directory of Map Projections

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Albers-Bonne homotopy

Parameters: Initial projection, Weight of terminal projection, Albers standard parallel 1, Albers standard parallel 2, Bonne standard parallel


A very configurable pseudoconic, equal-area projection that gives a continuum between Albers and Bonne projections. The standard parallels for the Albers and the Bonne projection do not result in standard parallels in the resulting projection, in general; they describe the source projections only.




Meridians: Complex curves except for straight central meridian.
Parallels: Portions of circles.
Poles: Points.


Initial projection: One of “Albers” or “Bonne”. The continuum of projections differs depending on the order.
Weight of terminal projection: 0 gives the initial projection; 1 gives the terminal projection; values between give and intermediate projection on the continuum.
Albers standard parallel 1: Configures the Albers as per its usual parameters.
Albers standard parallel 2: Configures the Albers as per its usual parameters.
Bonne standard parallel: Configures the Bonne as per its usual parameter.

Similar projections

The equal-area pseudoconic projection has many similar configurations.
Albers projection is a limiting form.
Bonne projection is a limiting form.


Presented by Daniel “daan” Strebe in 2017 as an example of a completely general system for producing a continuum, or “homotopy”, of equal-area projections between any two existing equal-area projections. This particular example was created to demonstrate how closely existing projections can be approximated by the technique—in this case, the equal-area pseudoconic projection, even though it was developed using very different methods.

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