Editing Cartogram (section)

==History==
[[File:Levasseur cartogram.png|thumb|upright=1.15|One of Levasseur's 1876 cartograms of Europe, the earliest known published example of this technique.]]
The cartogram was developed later than other types of [[Thematic map#History|thematic maps]], but followed the same tradition of innovation in [[France]].<ref>{{cite web
 | last = Johnson
 | title = Early cartograms
 | work = indiemaps.com/blog
 | date = 2008-12-08
 | url = http://indiemaps.com/blog/2008/12/early-cartograms/
 | access-date = 2012-08-17}}</ref> The earliest known cartogram was published in 1876 by French statistician and geographer [[Pierre Émile Levasseur]], who created a series of maps that represented the countries of Europe as squares, sized according to a variable and arranged in their general geographical position (with separate maps scaled by area, population, religious adherents, and national budget).<ref name="levasseur1876">{{cite journal |last1=Levasseur |first1=Pierre Émile |title=Memoire sur l'étude de la statistique dans l'enseignenent primaire, secondaire et superieur |journal=Programme du Neuvieme Congrès international de Statistique, I. Section, Theorie et population |date=1876-08-29 |pages=7–32 |url=https://babel.hathitrust.org/cgi/pt?id=uc1.c2558275}}. Unfortunately, all available scans did not expand the gatefold, so only one map in the series is visible online.</ref> Later reviewers have called his figures a statistical diagram rather than a map, but Levasseur referred to it as a ''carte figurative'', the common term then in use for any thematic map. He produced them as teaching aids, immediately recognizing the intuitive power of size as a visual variable: "It is impossible that the child is not struck by the importance of the trade of Western Europe in relation to that of Eastern Europe, that he does not notice how much England, which has a small territory but outweighs other nations by its wealth and especially by its navy, how much on the contrary Russia which, by its area and its population occupies the first rank, is still left behind by other nations in the commerce and navigation."

Levasseur's technique does not appear to have been adopted by others, and relatively few similar maps appear for many years. The next notable development was a pair of maps by [[Justus Perthes (publishing company)#Hermann Haack|Hermann Haack]] and Hugo Weichel of the [[1898 German federal election|1898 election results]] for the [[Reichstag of the German Empire|German Reichstag]] in preparation for the [[1903 German federal election|1903 election]], the earliest known ''contiguous cartogram''.<ref name="haack1903">{{cite book |last1=Haack |first1=Hermann |last2=Weichel |first2=Hugo |title=Kartogramm zur Reichstagswahl. Zwei Wahlkarten des Deutschen Reiches |date=1903 |publisher=Justus Perthes Gotha}}</ref> Both maps showed a similar outline of the German Empire, with one subdivided into constituencies to scale, and the other distorting the constituencies by area. The subsequent expansion of densely populated areas around [[Berlin]], [[Hamburg]], and [[Saxony]] was intended to visualize the controversial tendency of the mainly urban [[Social Democratic Party of Germany|Social Democrats]] to win the popular vote, while the mainly rural [[Centre Party (Germany)|Zentrum]] won more seats (thus presaging the modern popularity of cartograms for showing the same tendencies in recent elections in the United States).<ref name="hennig2018">{{cite journal |last1=Hennig |first1=Benjamin D. |title=Kartogramm zur Reichstagswahl: An Early Electoral Cartogram of Germany |journal=The Bulletin of the Society of University Cartographers |date=Nov 2018 |volume=52 |issue=2 |pages=15–25 |url=https://www.researchgate.net/publication/329880252}}</ref>

The continuous cartogram emerged soon after in the United States, where a variety appeared in the popular media after 1911.<ref name="bailey1911">{{cite journal |last1=Bailey |first1=William B. |title=Apportionment Map of the United States |journal=The Independent |date=April 6, 1911 |volume=70 |issue=3253 |page=722 |url=https://archive.org/details/independent70newy/page/722/mode/2up}}</ref><ref>{{cite journal |title=Electrical Importance of the Various States |journal=Electrical World |date=March 19, 1921 |volume=77 |issue=12 |pages=650–651 |url=https://archive.org/details/electricalworld77newy/page/650}}</ref> Most were rather crudely drawn compared to Haack and Weichel, with the exception of the "rectangular statistical cartograms" by the American master cartographer [[Erwin Raisz]], who claimed to have invented the technique.<ref name="raisz1934">{{cite journal |last1=Raisz |first1=Erwin |title=The Rectangular Statistical Cartogram |journal=Geographical Review |date=Apr 1934 |volume=24 |issue=2 |pages=292–296 |doi=10.2307/208794|jstor=208794 |bibcode=1934GeoRv..24..292R }}</ref><ref name="raisz1936">{{cite journal |last1=Raisz |first1=Erwin |title=Rectangular Statistical Cartograms of the World |journal=[[Journal of Geography]] |date=1936 |volume=34 |issue=1 |pages=8–10 |doi=10.1080/00221343608987880|bibcode=1936JGeog..35....8R }}</ref>

When Haack and Weichel referred to their map as a ''kartogramm'', this term was commonly being used to refer to all thematic maps, especially in Europe.<ref name="funkhouser1937">{{cite journal |last1=Funkhouser |first1=H. Gray |title=Historical Development of the Graphical Representation of Statistical Data |journal=Osiris |date=1937 |volume=3 |pages=259–404 |doi=10.1086/368480 |jstor=301591 |s2cid=145013441 |url=https://www.jstor.org/stable/301591|url-access=subscription }}</ref><ref name="krygier2010">{{cite web |last1=Krygier |first1=John |title=More Old School Cartograms, 1921-1938 |url=https://makingmaps.net/2010/11/30/more-old-school-cartograms-1921-1938/ |website=Making Maps: DIY Cartography |date=30 November 2010 |access-date=14 November 2020}}</ref> It was not until Raisz and other academic cartographers stated their preference for a restricted use of the term in their textbooks (Raisz initially espousing ''value-area cartogram'') that the current meaning was gradually adopted.<ref name="raisz">Raisz, Erwin, ''General Cartography'', 2nd Edition, McGraw-Hill, 1948, p.257</ref><ref name="raisz1962">{{cite book |last1=Raisz |first1=Erwin |title=Principles of Cartography |date=1962 |publisher=McGraw-Hill |pages=215–221}}</ref>

The primary challenge of cartograms has always been the drafting of the distorted shapes, making them a prime target for computer automation. [[Waldo R. Tobler]] developed one of the first algorithms in 1963, based on a strategy of warping space itself rather than the distinct districts.<ref name="tobler1963">{{cite journal |last1=Tobler |first1=Waldo R. |title=Geographic Area and Map Projections |journal=Geographical Review |date=Jan 1963 |volume=53 |issue=1 |pages=59–79 |doi=10.2307/212809|jstor=212809 |bibcode=1963GeoRv..53...59T }}</ref> Since then, a wide variety of algorithms have been developed (see below), although it is still common to craft cartograms manually.<ref name="tobler2004"/>