A method of illustrating three-dimensional spherical data in two dimensions. The point with spherical polar coordinates (1, θ, ϕ) is represented by the point with polar coordinates (d, ϕ), where, for 0°≤θ≤ 90°,The quantity d is the (chordal) distance from the pole at θ=0°. Data having θ > 90° are plotted in the same way, using either a different diagram, or a different plotting symbol, and replacing sin(½θ) with cos(½θ); the distance is now taken from the opposite pole at θ=180°.