Visualization of epidemiological information using area cartograms or density equalized maps
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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

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

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.


Us presidential election 2004

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)


Application in epidemiology

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


Application 1 salmonella surveillance

Application 1:Salmonella surveillance

- without cartogram

  • Shading = density of cattle holdings

  • Dot density = cases

  • Dot density = cases


Application 1 salmonella surveillance1

Application 1:Salmonella surveillance

- using cartogram

  • Area = number of cattle holdings

  • Shading = cattle per holding

  • Dot density = cases

Birch, C.P.D. (2008)


Application 2 scrapie surveillance

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)


Benefits of area cartograms in epidemiology

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


Cartogram methods and tools are readily available

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


Other references

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.


Visualization of epidemiological information using area cartograms or density equalized maps

Visualization of epidemiological information using area cartograms or density-equalized mapsColin Birch

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