Cartographic Projection
every map is wrong, and by exactly how much
Concept

Lambert cylindrical — where it appears

The cylindrical projection whose northing is the sine of the latitude, which makes it equal-area exactly. It carries the same sec²φ of distortion as Mercator and puts all of it into shape rather than into area, which is why it is the natural base for a cartogram.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

Four cities, met — the triangular, x first construction. Every cell drawn here holds the same area of ground and a different area of page: the map has been constructed so that its areal scale factor is the density it was handed, cell by cell, over a contrast of 25.99 to one. The residual against that target is 5.1e-6, measured from the map's own derivatives rather than from the construction. What it cost is the shape: the redistribution alone reaches 139.1° of angular deformation and averages 70.4°, on top of whatever the equal-area projection under it was already doing.

A map drawn to a density it was handed

Two hundred and twenty-six essays measure distortion after the fact. This one specifies it: a density is handed to a map as a boundary condition, the areal scale factor comes out equal to it to five parts in a million, and every other invariant the site owns becomes the price.

distortion · Cartogram Two conventions for one indicatrix field on Mercator. The left panel is the convention nearly every published field uses: every ellipse drawn at the same area on the paper, so the picture carries the shape and throws the size away. The right panel draws the image of the same ground circle at every place, so the drawn area IS the areal scale factor. On Mercator the axis ratio spans 1.0000 and the areal factor spans 14.93, so the left panel shows nothing the other one shows. Neither caption states which is which, on any published map this collection has found.

The ellipses are a sample, drawn at a size somebody chose

Thirteen essays measure with the indicatrix and none audits it as an instrument. A published field has a gauge nobody states and a placement nobody states: on Mercator the standard convention draws twenty-five identical circles while the areal factor runs over a factor of 14.9, and the average a reader takes off any of these fields is between 22 and 64 per cent too high.

distortion · Tissot

Named alongside it

The objects these essays reach for when they reach for this one.

Angular deformationAreal factorEqual-areaPrincipal scale factorsBoundary conditionCartogramConformalityDensityGraticuleInstrumentJacobianMercator

All concepts