Also knowns as a Levasseur Cartogram, Square Cartogram.

A Demers Cartogram is a Cartogram variation where each geographical region is represented by a square, with the area of the square proportional to the data value being visualised geographically.

The organisation of the squares is loosely based on the original topology to avoid any overlapping. A Demers Cartogram aims to reduce the gaps between adjacent squares compared to Dorling Cartograms (which use circles instead) — this helps to provide a more contiguous appearance.

Tools to generate this chart with:
ArcGIS
D3.js, Chris Given’s Github
Datawrapper

Examples

One of a series of cartograms of Europe published in 1876 by Pierre Émile Levasseur, the earliest known cartograms ever produced.
Congrès international de statistique (9th : 1876 : Budapest, Hungary)