ENV 2006 10.1

Envisioning Information

Lecture 10 – Cartograms: A different way of drawing maps

Ken Brodliekwb@comp.leeds.ac.uk

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.