Multivariate thematic maps found a resurgence starting in the middle of the 20th Century, coinciding with the scientific turn in geography. George F. Jenks introduced the bivariate dot density map in 1953. The first modern bivariate choropleth maps were published by the U.S. Census Bureau in the 1970s. Their often complex patterns of multiple colors has drawn acclaim and criticism ever since, but has also led to research to discover effective design techniques.
