Junk Charts

Flight of fancy

The venerable Wired magazine has surely gone too far with this flight of fancy!  Consider:

• The zig-zagging lines streaming across the map
• The redundant white dots, each of equal size, contradicting the black dots, with size proportional to prevalence
• The inexplicable use of 00, 01, 02, ...
• The use of a taller column for human cases, when tallied, amounting  to about 1/20 the number for bird cases
• The inclusion of Australia (with zero cases) while excluding the Americas (also zero cases)
• Ordering the countries neither by bird nor human cases but by convenience of placement on the map

As with a previous example, the map adds nothing to the data except for providing a lesson in geography.  We prefer a parallel bar chart, shown on the right.  Here, the continents are given different colors.  In an unusual move, I chose different scales for each side as I am more interested in the distribution among countries, rather than the relative prevalence of bird/human cases.

Reference: "Flight H5N1: Delayed", Wired Magazine, October 2006.

Finding dots

Erik W. alerted me to this CNN map that shows FBI statistics about safety of American cities.  As Eric pointed out, this is prototypical of chartjunk a la Tufte.  A lot of ink is used to depict 12 points of data (top 3 cities in safety, crime, improvement and decline).

Imagine the reader trying to find the 3rd most improved city.  She either has to find all the blue dots and then figure out which is #3; or she needs to find all the #3 dots and figure out which is blue.  As they say, it's "hard work".  In fact, finding the dots among the forest of large text is hard work by itself!

How would I re-make this chart?

• Highlight only the states containing data (California, Michigan, Missouri, Ohio, Georgia, New Jersey, New York); gray out all other states and their boundaries
• Separate the states from the cities; only write the State name once for each State; reduce the font size
• Instead of dots, use numbers.  So the most dangerous city (St Louis) gets a red "1", Oakland gets a purple "3", etc.
• Remove Mexico, Canada and water from the map

The map gives the false impression that crime is relevant only along the coasts and the lakes, when in fact, the map is just saying that most cities in the U.S. are located along the coasts and the lakes.  Using such a map to depict city-level statistics creates distortion because cities are not evenly distributed across America.

Beyond that, what is the point of this map?  Is it merely a geography class telling us where each city is located?  How is it better than a simple table listing the cities in order?   

Reference: "U.S. City Safety Rankings", CNN, 2006.

Small and beautiful

The creater of this map understands small is beautiful: simple concepts deserve simple charts.

As discussed in the NYT article, Allegiant's business model is small and beautiful -- rather than focusing on popular routes between major cities like most startup airlines, Allegiant serves a web of routes going to just two destinations.

In this map, the two destinations are clearly labeled; all the originating cities are marked with those serving both Las Vegas and Orlando highlighted.  Extra information is provided through shading of the States served, and through the route lines (roughly indicating distance / time).

This simple chart can be made simpler by removing the route lines.  Not much is lost by removing them.

Reference: "Flying Where Big Airlines Aren't", New York Times, Sep 21 2006.

Tracks

"Tropical Storm Debby strengthened as it moved northwest yesterday.  Of the 15 previous storms with positions similar [...], 13 became hurricanes, but only two reached the United States".

This data-laden statement accompanied the following weather map.

Now.  Imagine if:

• no colors were used, and
• the two storms that landed had tracks bolded, and
• the 13 hurricanes had solid tracks, and
• all other tracks were drawn gray, and
• the then location of Debby was annotated, and
• only the two making landfall (Gloria 1985 and Storm 4 1938) were labelled, and
• the locations of landfall were crossed, and
• the large box was removed, revealing the land mass,
  

Then only the key data needed to support the accompanying statement would be present.

Reference: "Highlight: Tropical Storm Debby", New York Times (weather report),  Aug 24 2006

Choke points

The following map highlights in color the stretches of major roads in the New York area that experience congestion.

A couple of improvements can be made:

• The smaller roads should be left out completely rather than dimmed; as noted in the text box, congestion on smaller roads is ignored
• More than two colors will bring out the difference between different roads better; as it stands, it is hard to see that 78 is the most congested.  With more colors, the annotation would be rendered unnecessary

Reference: "The Next Thing in Tolls?", New York Times, June 14, 2006

Rising bankruptcies

It was quite exciting to see this nice map in the Sunday Times:
 

Actual headline for the map: "Where Home Prices Rise Sharply, Bankruptcies Fall"

Alternative headline for the map: "Bankruptcies Jump in the South and Midwest"

Not clear from this map (but mentioned in the article):

• A new law, effective Oct 17, which will make it harder to clear away credit card debt has touched off "a rush to the court" (This effect would have happened in 2005 so would be hidden in 2000-2005 changes.)
  
• There is "strong evidence" that home equity borrowing is providing a further bulwark against disaster although the author also cites an economist saying that unemployment rates, not house prices, tend to be the most important predictors of bankruptcy

The map'd be even nicer if the element of population density can be added to it although I am not sure how this can be done without producing clutter.  Do make a suggestion in the comments if you have an idea.  Such a map would then adjust for the problem of "low populations" as indicated in the very useful note on the map.

I'll also repeat a previously mentioned point, which is that the legend should mark out the actual maximum and minimum of the data, rather than using "greater than 35%".

Reference: "Where Home Prices Rise Steeply. Bankruptcies Fall", New York Times, Oct 9 2005.

More mischief in map coloring

Sam Cook was nice enough to mention Junk Charts on her and Andrew Gelman's blog today.  She provided another example of mischievous use of colors and shading in data maps, showing that sometimes we statisticians are no better than the rest. The effect is quite innocently hilarious and is a must-see!

Instead of assigning each level to a different color/shade, the geographical pattern of Amstat meetings is more clearly revealed if a different shade was used for 0, 1-2, 3-5, 7.  Thus:
 

Obesity bad, maps good

The recent coverage of obesity in the US media produced at least two very good data maps.  The New York Times printed this snapshot of the nation in 2004.

Because of a judiciously chosen color scheme, we can easily discern the pattern of obesity: more severe between the Lakes and the Gulf; least in the West and Northeast, especially in Colorado; quite bad in the middle and the South.

The legend is deserving of much praise:   in defiance of popular but simplistic usage, the range was not divided into four equal parts (quartiles); rather, the designer selected four unequal parts so as to reveal the geographical pattern on the map. Besides, the complete range of the data was shown as is, where most would have artificially widened the range to 15.0% on one end and 30.0% on the other.

All in all, this is a simple graphic conveying a clear message.  Well done.

And yet -- the dynamic aspect of obesity growth alarms even more:

• Within many states, more and more people are becoming obese
• Nationally, more and more states have high obesity rates

These trends, along with others, are perfectly captured by the following terrific, dynamic data map, thanks to CDC.  It is a wonderful example of how the electronic medium (animated gif) can do wonders for the graphics designer. [You may need to click on the map to see the animation in a pop-up window.]

The time dimension is experienced rather than drawn on paper/screen.  This experience is in fact distorted, compressed time is what we feel, but the distortion improves rather than deter our ability to see trends.

• The states between the Lakes and the Gulf led the nation throughout this period.
• The ever expanding legend ingeniously draws attention to the fact that the worst states have gotten worse over time.
• No single state has been spared: by 2001, only Colorado had an obesity rate below 15%; just 7 years earlier, in 1994, the entire Western half of the U.S. had obesity rates below 15%.

One small gripe: if read quickly, the reader can be forgiven for thinking that "white" indicates 0% obesity.  Not so!  "White" actually means "no data".  I'd prefer to use a neutral color for "no data"; when they started tracking, these states turned out to be no less obese than others.  By 1994, every state has started tracking obesity.

This dynamic map is really rich in information.  Feel free to leave comments about what else strikes you about it.

Reference: "Obesity Rate Is Nearly 25%, Group Said", New York Times, August 24, 2005; CDC Obesity Trends.