Equal area projection — where it appears
Named by 3 essays across one field — each of them below, with the objects they name alongside it.
Every fisheye is a different rule
The word "fisheye" names a shape of lens and not a projection. There are several, they disagree with each other by tens of per cent at the frame edge, and each is the right answer to a different question — one is a protractor, one is a counting instrument, one preserves shape. Which one a lens implements is a fact about that lens, and it is rarely printed on the barrel.
Conformal is not undistorted
The most distorted-looking picture in ordinary circulation is the little planet — a 360 photograph re-projected from below, with the ground curled into a ball. Its worst angular error over 160 degrees of the sphere is 4.4e-8 degrees, which is arithmetic noise. Every crossing in the original crosses at exactly the same angle in the result, and what has gone is area, over a factor of 255.
The lines a surface leaves alone
Only the plane draws every straight line straight, which this site has measured and which gets read as though a curved surface bent everything. It does not. Every curved picture surface here keeps a one-parameter family of world lines exactly straight, and the family is a curve on the sphere of lines rather than a region of it — so a grid of samples finds none of it, which is what the first version of this measurement reported.
Named alongside it
The objects these essays reach for when they reach for this one.
AnisotropyArea scaleConformalDemonstrationEquidistant projectionEquirectangularfield of viewnecessary, not sufficientPicture surfaceStereographic projectionBeltramiCanopy photography