visualization of epidemiological information using area cartograms or density-equalized maps
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Visualization of epidemiological information using area cartograms or density-equalized mapsC.P.D. Birch
Centre for Epidemiology & Risk Analysis,
Veterinary Laboratories Agency – Weybridge,
Surrey, UK
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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.
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US Presidential Election 2004
Unit = areaThis may be how ex-President Bush would like us to see the 2004 US Presidential Election result.
Unit = votersThis is a better representation of how The US population voted.
M. T. Gastner, C. R. Shalizi, and M. E. J. Newman (2004)
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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
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Shading = density of cattle holdings
Application 1:Salmonella surveillance
- without cartogram
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Truro
Thirsk
Preston
Penrith
Lasswade
Langford Weybridge
Starcross
Newcastle
Winchester
Shrewsbury
Luddington
Carmarthen
AberystwythBury St Edmunds
Sutton Bonington
London
Liverpool
Ayr
Perth
Thurso
Aberdeen
Dumfries
Inverness
Edinburgh
St Boswells
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X
X XX
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Truro
Thirsk
Preston
Penrith
Lasswade
Langford Weybridge
Starcross
Newcastle
Winchester
Shrewsbury
Luddington
Carmarthen
AberystwythBury St Edmunds
Sutton Bonington
London
Liverpool
Ayr
Perth
Thurso
Aberdeen
Dumfries
Inverness
Edinburgh
St Boswells
Dot density = cases Dot density = cases
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Thirsk
Preston
Penrith
Lasswade
LangfordWeybridge
Starcross
Newcastle
Winchester
Shrewsbury
Luddington
Carmarthen
Aberystwyth
Bury St Edmunds
Sutton Bonington
London
Liverpool
Ayr
Perth
Thurso
Aberdeen
Dumfries
Inverness
Edinburgh
St Boswells
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Starcross
Newcastle
Winchester
Shrewsbury
Luddington
Carmarthen
Aberystwyth
Bury St Edmunds
Sutton Bonington
London
Liverpool
Ayr
Perth
Thurso
Aberdeen
Dumfries
Inverness
Edinburgh
St Boswells
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""
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"
"
"")
")
X
X X
X
X
XX
X
")
")
Truro
Thirsk
Preston
Penrith
Lasswade
LangfordWeybridge
Starcross
Newcastle
Winchester
Shrewsbury
Luddington
Carmarthen
Aberystwyth
Bury St Edmunds
Sutton Bonington
London
Liverpool
Ayr
Perth
Thurso
Aberdeen
Dumfries
Inverness
Edinburgh
St Boswells
Shading = cattle per holding
Application 1:Salmonella surveillance
Birch, C.P.D. (2008)
Salmonella Incidents
! 1 Dot = 1 incident
! Locations randomized within counties
Area Representing 1000 Holdings
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Number of Cattle / Holding
2 - 30
31 - 60
61 - 90
91 - 120
121 - 150
151 - 250
" VLA Regional Laboratory
") VLA Surveillance Centre
X SAC Disease Surveillance Centre
- using cartogram
Area = number of cattle holdings
Dot density = cases
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Area = number of sheep holdings
Application 2:Scrapie surveillance
5000
% Holdings Sampled
0.0% - 1.5%
1.6% - 5.0%
5.1% - 20.0%
20.1% - 50.0%
> 50.0%
Scrapie cases detected
Classical
Atypical
Birch, C.P.D., Chikukwa, A.C., Hyder, K., Del Rio Vilas, V.J. (2009)
Shading = % holdings sampled
Dot density = cases
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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
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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
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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 Systems 8, 117-123.
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Visualization of epidemiological information using area cartograms or density-equalized maps
Colin Birch
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