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Visualization of epidemiological information using area cartograms or density-equalized maps

Visualization of epidemiological information using area cartograms or density-equalized maps. C.P.D. Birch Centre for Epidemiology & Risk Analysis, Veterinary Laboratories Agency – Weybridge, Surrey, UK. Introduction. Land area is irrelevant to many epidemiological presentations.

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Visualization of epidemiological information using area cartograms or density-equalized maps

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  1. Visualization of epidemiological information using area cartograms or density-equalized maps C.P.D. Birch Centre for Epidemiology & Risk Analysis, Veterinary Laboratories Agency – Weybridge, Surrey, UK

  2. Introduction • Land area is irrelevant to many epidemiological presentations. • So why use it to determine the size of mapping units? • Area cartograms provide an alternative. • Base the size of mapping units on measures that matter.

  3. US Presidential Election 2004 Unit = area This may be how ex-President Bush would like us to see the 2004 US Presidential Election result. Unit = voters This is a better representation of how The US population voted. M. T. Gastner, C. R. Shalizi, and M. E. J. Newman (2004)

  4. Application in epidemiology • Area of mapping units = target population. • Hence automatic visual weighting based on population distribution. • Shading = • Case density • Sampling distribution • or Other relevant factors • Dot density = cases

  5. Application 1:Salmonella surveillance - without cartogram • Shading = density of cattle holdings • Dot density = cases • Dot density = cases

  6. Application 1:Salmonella surveillance - using cartogram • Area = number of cattle holdings • Shading = cattle per holding • Dot density = cases Birch, C.P.D. (2008)

  7. Application 2:Scrapie surveillance 5000 • Area = number of sheep holdings • Shading = % holdings sampled • Dot density = cases Birch, C.P.D., Chikukwa, A.C., Hyder, K., Del Rio Vilas, V.J. (2009)

  8. Benefits of area cartograms in epidemiology • Better presentation of cases vs. denominator population • Direct visualization showing whether cases are uniformly or unevenly distributed. • Visual impression more accurate. • Richer data presentation • More data can be presented. • More space on the map for areas likely to contain more information. • Precise locations obscured (confidentiality) • Maps that emphasize features that matter

  9. Cartogram methods and tools are readily available • Downloads for ArcGIS • ESRI Cartogram and Geoprocessing Tool (Tom Gross, http://arcscripts.esri.com) • Cartogram Creator – used here (Eric Wolf, http://arcscripts.esri.com) • Method • Gastner & Newman (2004) Proc. NAS 101: 7499-7504 • Website • www.worldmapper.org

  10. Other references • Birch, C.P.D., 2008. Methods for spatial visualization by using maps in animal health surveillance. Veterinary Laboratories Agency, Report to Defra pp. 35. • Birch, C.P.D., Chikukwa, A.C., Hyder, K., Del Rio Vilas, V.J., 2009. Spatial distribution of the active surveillance of sheep scrapie in Great Britain: an exploratory analysis. BMC Veterinary Research 5, 23. • Gastner, M.T., Shalizi, C.R., Newman, M.E.J., 2005. Maps and cartograms of the 2004 US presidential election results. Advances in Complex Systems8, 117-123.

  11. Visualization of epidemiological information using area cartograms or density-equalized mapsColin Birch • To start presentation click arrow at bottom right.

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