Cartogram

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Kartenanamorphote (not Kartogramm) of Germany, with the states and districts resized according to population.

A cartogram is a map in which some thematic mapping variable – such as travel time, population, or Gross National Product – is substituted for land area or distance. The geometry or space of the map is distorted in order to convey the information of this alternate variable. There are two main types of cartograms: area and distance cartograms. Cartograms have a fairly long history, with examples from the mid-1800s.[1]

Area cartograms[edit]

Area cartogram of the United States, with each county rescaled in proportion to its population. Colors refer to the results of the 2004 U.S. presidential election popular vote.

An area cartogram is sometimes referred to as a value-by-area map or an isodemographic map, the latter particularly for a population cartogram, which illustrates the relative sizes of the populations of the countries of the world by scaling the area of each country in proportion to its population; the shape and relative location of each country is retained to as large an extent as possible, but inevitably a large amount of distortion results. Other synonyms in use are anamorphic map, density-equalizing map and Gastner map.[2][3][4]

Area cartograms may be contiguous or noncontiguous. The area cartograms shown on this page are all contiguous, while a good example of a noncontiguous cartogram was published in The New York Times.[5][6] The online resource SHOW®, provided by Mapping Worlds, creates discontiguous cartograms for different geographies (United States, Japan and World at this time) interactively, allowing users to quickly compare various characteristics. This method of cartogram creation is sometimes referred to as the projector method or scaled-down regions.

Cartograms may be classified also by the properties of shape and topology preservation. Classical area cartograms (shown on this page) are typically distorting the shape of spatial units to some degree, but they are strict at preserving correct neighborhood relationships between them. Scaled-down cartograms (from the NY Times example) are strictly shape-preserving. Another branch of cartograms introduced by Dorling, replaces actual shapes with circles scaled according to the mapped feature. Circles are distributed to resemble the original topology. Demers cartogram is a variation of Dorling cartogram, but it uses rectangles instead of circles, and attempts to retain visual cues at the expense of minimum distance. Schematic maps based on quad trees can be seen as non shape-preserving cartograms with some degree of neighborhood preservation.

A collection of about 700 contiguous area cartograms is available at Worldmapper,[7] a collaborative team of researchers at the Universities of Sheffield and Michigan.

Production[edit]

Cartogram showing Open Europe estimate of total European Union per capita net budget expenditure in euros for the whole period 2007-2013 per capita, based on Eurostat 2007 pop. estimates (Luxembourg not shown).
Net contributors
  -5000 to -1000 euro per capita
  -1000 to -500 euro per capita
  -500 to 0 euro per capita
Net recipients
  0 to 500 euro per capita
  500 to 1000 euro per capita
  1000 to 5000 euro per capita
  5000 to 10000 euro per capita
  10000 euro plus per capita
  n/a

One of the first cartographers to generate cartograms with the aid of computer visualization was Waldo Tobler of UC Santa Barbara in the 1960s. Prior to Tobler's work, cartograms were created by hand (as they occasionally still are). The National Center for Geographic Information and Analysis located on the UCSB campus maintains an online Cartogram Central with resources regarding cartograms.

A number of software packages generate cartograms. Most of the available cartogram generation tools work in conjunction with other GIS software tools as add-ons or independently produce cartographic outputs from GIS data formatted to work with commonly used GIS products. Examples of cartogram software include ScapeToad,[8][9] Cart,[10] and the Cartogram Processing Tool (an ArcScript for ESRI's ArcGIS), which all use the Gastner-Newman algorithm.[11][12]

Cartogram Algorithms[edit]

Year Author Algorithm name Cartogram type Shape preserving
1973 Tobler Rubber map method area contiguous with distortion
1976 Olson Projector method area noncontiguous yes
1978 Kadmon, Shlomi Polyfocal projection distance radial
1984 Selvin et al. DEMP (Radial Expansion) method area contiguous with distortion
1985 Dougenik et al. Rubber Sheet Distortion method area contiguous with distortion
1986 Tobler Pseudo-Cartogram method area contiguous with distortion
1987 Snyder Magnifying glass azimuthal map projections distance radial
1989 Cauvin et al. Piezopleth maps area contiguous with distortion
1990 Torguson Interactive polygon zipping method area contiguous with distortion
1990 Danny Dorling Cellular Automata Machine method area contiguous with distortion
1993 Gusein-Zade, Tikunov Line Integral method area contiguous with distortion
1996 Dorling Circular cartogram area noncontiguous no (circles)
1997 Sarkar, Brown Graphical fisheye views distance radial
1997 Edelsbrunner, Waupotitsch Combinatorial-based approach area contiguous with distortion
1998 Kocmoud, House Constraint-based approach area contiguous with distortion
2003 Keim, North, Panse Cartodraw area contiguous with distortion
2003 Keim, North, Panse HistoScale area contiguous with distortion
2004 Gastner, Newman Diffusion-based method area contiguous with distortion
2004 Sluga Lastna tehnika za izdelavo anamorfoz area contiguous with distortion
2004 Helimann, Keim et al. RecMap area contiguous no (rectangles)
2005 Keim, North, Panse Medial-axis-based cartograms area contiguous with distortion
2007 van Kreveld, Speckmann Rectangular Cartogram area contiguous no (rectangles)
2009 Heriques, Bação, Lobo Carto-SOM area contiguous with distortion
2014 B. S. Daya Sagar Mathematical Morphology-Based Cartograms area contiguous with distortion in local shapes and with no distortion in global shape

See also[edit]

References[edit]

  1. ^ Johnson (2008-12-08). "Early cartograms". indiemaps.com/blog. Retrieved 2012-08-17. 
  2. ^ Michael T. Gastner; Mark E. J. Newman (2004). "Diffusion-based method for producing density equalizing maps". Proceedings of the National Academy of Sciences 101 (20): 7499–7504. arXiv:physics/0401102. Bibcode:2004PNAS..101.7499G. doi:10.1073/pnas.0400280101. PMC 419634. PMID 15136719. 
  3. ^ Gallery of Data Visualization - Bright Ideas
  4. ^ UNEP GRID Ardenal: Anamorphic Maps
  5. ^ Johnson (2011-02-22). "Noncontiguous cartograms in OpenLayers and Polymaps". indiemaps.com/blog. Retrieved 2012-08-17. 
  6. ^ Cowan, Sarah; Doyle, Stephen; Heffron, Drew (2008-11-02), "Op-Chart: How Much Is Your Vote Worth?", New York Times, retrieved 2012-08-17 
  7. ^ Worldmapper:The world as you've never seen it before
  8. ^ ScapeToad
  9. ^ The Art of Software: Cartogram Crash Course
  10. ^ Cart: Computer software for making cartograms
  11. ^ Cartogram Geoprocessing Tool version 2
  12. ^ Hennig, Benjamin D.; Pritchard, John; Ramsden, Mark; Dorling, Danny, "Remapping the World's Population: Visualizing data using cartograms", ArcUser (Winter 2010): 66–69 

Further reading[edit]

External links[edit]