Cartograms - Images of the social and economic world
Here is an ordinary map of the world:
Click on image for a larger version
Roughly speaking, on a map like this, the sizes of the countries of the
world are in proportion to their actual sizes on the surface of the planet
and their shapes are the same as their actual shapes. (This is only
approximate though, since some distortion is inevitable when you go from a
spherical planet to a flat map.)
It's possible, however, and sometimes very useful, to redraw the map with
the sizes of countries made bigger or smaller in order to represent something
of interest. Such maps are called cartograms and can be an effective
and natural way of portraying geographic or social data.
Here, for example, is a cartogram that shows the human population of the
countries of the world:
Population
Click on image for a larger version
In this map the sizes of countries are proportional not to their actual
landmass but instead to the number of people living there; a country with 20
million people, for instance, appears twice as large as a country with 10
million.
Although the figures for populations of countries are well established and
familiar to many, the cartogram provides a new way of looking at them and in
particular makes clear the enormous disparity in the population of different
regions. Note how large India and China have become: between them these two
countries account for more than a third of the population of the world. On
the other hand, notice the near-disappearance of Canada and Russia, the
world's two largest countries by land area, which have relatively few people
in them.
Notice also how the lines of latitude and longitude have become distorted
by the growing and shrinking countries. This is an unavoidable consequence of
the cartogram transformation: in order to give the countries the right sizes
and still have them fit together you need to warp things a bit. The method
used here, however, does a pretty good job of keeping the map recognizable.
Cartograms are most often used to show population data, but there is no
reason why they need be limited to population. They can in principle be used
to show almost any quantity. Here is a cartogram of the world in which the
sizes of countries are proportional to Gross Domestic Product, which is a
measure of how much wealth a country's economy generates, and hence, to an
extent, of the wealth of the country's inhabitants:
Gross domestic product
Click on image for a larger version
Notice how America and Europe dominate this map, along with Japan (yes –
that huge dark-green island on the right really is Japan), while Africa
dwindles almost to invisiblity.
Now here are a few more cartograms. In all of the maps on this page the
countries have the same colors, which helps to identify countries in the
cases where shapes have changed a lot.
Child mortality
Click on image for a larger version
People living with HIV/AIDS
Click on image for a larger version
Total spending on healthcare
Click on image for a larger version
Energy consumption (including oil)
Click on image for a larger version
Greenhouse gas emissions
Click on image for a larger version
Technical details: These cartograms were created
using a variant of the
diffusion
algorithm of Gastner and Newman. Data for the population cartogram were
taken from the
Gridded
Population of the World compiled by the International Center for Earth
Science at Columbia University; elevation and bathymetric data were taken
from the NOAA
2-minute Gridded Global Relief data set. Data for the other cartograms
came from the
United Nations
Statistics Division and from the databases of the
World Health Organization. In
all of the cartograms on this page, Antarctica has been treated the same as
the sea, meaning its area is unchanged although its shape may be distorted
slightly to make room for changes in the sizes of other parts of the world.
link to
original page
© 2006 M. E. J. Newman -
Mark Newman, Department
of Physics and Center for the Study of Complex Systems, University of
Michigan
Email: mejn@umich.edu - Updated: February 16, 2006
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