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Fig. 3.
Napoleon's March on Moscow depicted by M. Minard [12]. Width indicates the
number of soldiers. Temperature during the retreat is presented below the map.
Image
courtesy of Ecole Nationale des Ponts et Chaussees
.
soldiers) as well as the devastating effect of crossing the Berezina river (50,000
soldiers before, 25,000 after). The depiction confirms that Napoleon lost the
invasion (a well known fact) and reveals many other facts, such as the continuous
death rate due to disease and the “scorched earth” tactics of Russia instead of
specific death tolls of large battles.
John Snow's map was made to answer the question: “What is the origin of the
London cholera epidemics?”. Contrary to the previous map, the answer requires
some thinking. Black rectangles indicate location of deaths. At the center of the
infected zone lies a water pump that John Snow found to be responsible for the
infection. Once again, choosing the right representation was essential for finding
the answer. As a side-effect, the map reveals the magnitude of the epidemic.
Figure 1 answers the question: “Is there a relationship between income and
college degree?” by showing a scatter plot of income by degree for each US state.
The answer is the obvious: yes, but there is much more. There seems to be a
linear correlation between them and some outliers such as Nevada (likely due to
Las Vegas) and Utah do exist, raising new unexpected questions.
Information Visualization couples interaction and visual representation so its
power is better demonstrated interactively. The simplest demonstration suited
to the largest audience is probably the Dynamic HomeFinder
5
[32].Itshowsthe
map of the Washington D.C. area overlaid with all the homes for sale (Figure 5).
Dynamic queries implemented by sliders and check-boxes interactively filter-out
homes that do not fit specific criteria such as cost or number of bedrooms.
Using the interactive controls, it becomes easy to find homes with the desired
attributes or understand how attributes' constraints should be relaxed to find
some matching homes. Unexpectedly, the Dynamic HomeFinder also reveals the
5
http://www.cs.umd.edu/hcil/pubs/dq-home.zip
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