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ENV 2006 10.1
Envisioning Information
Lecture 10 – Cartograms: A different way of drawing maps
ENV 2006 10.2
Choropleth Maps
• Maps have been traditionally drawn to represent area
– With topography indicated by shading
• Increasingly we use maps to represent properties about areas
– Here each state is shaded according to density of population
– Known as choropleth mapping
http://www.cdc.noaa.gov/USclimate/states.fast.html
ENV 2006 10.3
Discuss Strengths and Weaknesses
• Strengths • Weaknesses
ENV 2006 10.4
Cartograms
• The cartogram is a response to these issues
– Rather than accurately reflect the area and superimpose shading to represent the variable..
– .. Distort the area so as to reflect the variable directly
ENV 2006 10.5
Types of Cartogram
• Cartograms can be contiguous or non-contiguous
– Here is population of California by county as a contiguous cartogram
ENV 2006 10.6
Types of Cartogram
• .. And now as a non-contiguous cartogram
ENV 2006 10.7
Contiguous and Non-Contiguous Cartograms
• Here is the US population example in both styles…
ENV 2006 10.8
Perimeter-preservation
ENV 2006 10.9
World Population Cartogram
Acknowledgement: Examples taken from Web site of Dr Donald Househttp://www-viz.tamu.edu/faculty/house/cartograms
ENV 2006 10.10
George Bush – Victory large or small?
ENV 2006 10.11
Types of Cartogram
• Danny Dorling (recently Professor in Leeds) invented a special type of cartogram using circles of different size
http://www.ncgia.ucsb.edu/projects/Cartogram_Central/index.html
ENV 2006 10.12
Dorling Cartograms
• Try the applet at:http://www.mapresso.com/dorling/dorlingexample.html
ENV 2006 10.13
British county populations evolving…
ENV 2006 10.14
Chernoff Face Cartogram!
• Acknowledgement:– Last two slides from
‘Cartograms for Human Geography’, by D. Dorling, in Visualization in Geographical Information Systems, Wiley.