## Much more to do after selecting a chart form

##### Mar 06, 2017

I sketched out this blog post right before the Superbowl - and was really worked up as I happened to be flying into Atlanta right after they won (well, according to any of our favorite "prediction engines," the Falcons had 95%+ chance of winning it all a minute from the end of the 4th quarter!) What I'd give to be in the SuperBowl-winning city the day after the victory!

Maybe next year. I didn't feel like publishing about SuperBowl graphics when the wound was so very raw. But now is the moment.

The following chart came from Orange County Register on the run-up to the Superbowl. (The bobble-head quarterbacks also came from OCR). The original article is here.

The choice of a set of dot plots is inspired. The dot plot is one of those under-utilized chart types - for comparing two or three objects along a series of metrics, it has to be one of the most effective charts.

To understand this type of design, readers have to collect three pieces of information: first is to recognize the dot symbols, which color or shape represents which object being compared; second is to understand the direction of the axis; third is to recognize that the distance between the paired dots encodes the amount of difference between the two objects.

The first task is easy enough here as red stands for Atlanta and blue for New England - those being the team colors.

The second task is deceptively simple. It appears that a ranking scale is used for all metrics with the top ("1st") shown on the left side and the bottom ("32nd") shown on the right. Thus, all 32 teams in the NFL are lined up left to right (i.e. best to worst).

Now, focus your attention on the "Interceptions Caught" metric, third row from the bottom. The designer indicated "Fewest" on the left and "Most" on the right. For those who don't know American football, an "interception caught" is a good defensive play; it means your defensive player grabs a ball thrown by the opposing team (usually their quarterback), causing a turnover. Therefore, the more interceptions caught, the better your defence is playing.

Glancing back at the chart, you learn that on the "Interceptions Caught" metric, the worst team is shown on the left while the best team is shown on the right. The same reversal happened with "Fumbles Lost" (fewest is best), "Penalties" (fewest is best), and "Points Allowed per Game" (fewest is best). For four of nine metrics, right is best while for the other five, left is best.

The third task is the most complicated. A ranking scale always has the weakness that a gap of one rank does not yield information on how important the gap is. It's a complicated decision to select what type of scale to use in a chart like this, and in this post, I shall ignore this issue, and focus on a visual makeover.

***

I find the nine arrays of 32 squares, essentially the grid system, much too insistent, elevating information that belongs to the background. So one of the first fixes is to soften the grid system, and the labeling of the axes.

In addition, given the meaningless nature of the rank number (as mentioned above), I removed those numbers and used team logos instead. The locations on the axes are sufficient to convey the relative ranks of the two teams against the field of 32.

Most importantly, the directions of all metrics are now oriented in such a way that moving left is always getting better.

***

While using logos for sports teams is natural, I ended up replacing those, as the size of the dots is such that the logos are illegible anyway.

The above makeover retains the original order of metrics. But to help readers address the key question of this chart - which team is better, the designer should arrange the metrics in a more helpful way. For example, in the following version, the metrics are subdivided into three sections: the ones for which New England is significantly better, the ones for which Atlanta is much better, and the rest for which both teams are competitive with each other.

In the Trifecta checkup (link), I speak of the need to align your visual choices with the question you are trying to address with the chart. This is a nice case study of strengthening that Q-V alignment.

## Political winds and hair styling

##### Nov 23, 2016

Washington Post (link) and New York Times (link) published dueling charts last week, showing the swing-swang of the political winds in the U.S. Of course, you know that the pendulum has shifted riotously rightward towards Republican red in this election.

The Post focused its graphic on the urban / not urban division within the country:

Over Twitter, Lazaro Gamio told me they are calling these troll-hair charts. You certainly can see the imagery of hair blowing with the wind. In small counties (right), the wind is strongly to the right. In urban counties (left), the straight hair style has been in vogue since 2008. The numbers at the bottom of the chart drive home the story.

Previously, I discussed the Two Americas map by the NY Times, which covers a similar subject. The Times version emphasizes the geography, and is a snapshot while the Post graphic reveals longer trends.

Meanwhile, the Times published its version of a hair chart.

This particular graphic highlights the movement among the swing states. (Time moves bottom to top in this chart.) These states shifted left for Obama and marched right for Trump.

The two sets of charts have many similarities. They both use curvy lines (hair) as the main aesthetic feature. The left-right dimension is the anchor of both charts, and sways to the left or right are important tropes. In both presentations, the charts provide visual aid, and are nicely embedded within the story. Neither is intended as exploratory graphics.

But the designers diverged on many decisions, mostly in the D(ata) or V(isual) corner of the Trifecta framework.

***

The Times chart is at the state level while the Post uses county-level data.

The Times plots absolute values while the Post focuses on relative values (cumulative swing from the 2004 position). In the Times version, the reader can see the popular vote margin for any state in any election. The middle vertical line is keyed to the electoral vote (plurality of the popular vote in most states). It is easy to find the crossover states and times.

The Post's designer did some data transformations. Everything is indiced to 2004. Each number in the chart is the county's current leaning relative to 2004. Thus, left of vertical means said county has shifted more blue compared to 2004. The numbers are cumulative moving top to bottom. If a county is 10% left of center in the 2016 election, this effect may have come about this year, or 4 years ago, or 8 years ago, or some combination of the above. Again, left of center does not mean the county voted Democratic in that election. So, the chart must be read with some care.

One complaint about anchoring the data is the arbitrary choice of the starting year. Indeed, the Times chart goes back to 2000, another arbitrary choice. But clearly, the two teams were aiming to address slightly different variations of the key question.

There is a design advantage to anchoring the data. The Times chart is noticeably more entangled than the Post chart. There are tons more criss-crossing. This is particularly glaring given that the Times chart contains many fewer lines than the Post chart, due to state versus county.

Anchoring the data to a starting year has the effect of combing one's unruly hair. Mathematically, they are just shifting the lines so that they start at the same location, without altering the curvature. Of course, this is double-edged: the re-centering means the left-blue / right-red interpretation is co-opted.

On the Times chart, they used a different coping strategy. Each version of their charts has a filter: they highlight the set of lines to demonstrate different vignettes: the swing states moved slightly to the right, the Republican states marched right, and the Democratic states also moved right. Without these filters, the readers would be winking at the Times's bad-hair day.

***

Another decision worth noting: the direction of time. The Post's choice of top to bottom seems more natural to me than the Times's reverse order but I am guessing some of you may have different inclinations.

Finally, what about the thickness of the lines? The Post encoded population (voter) size while the Times used electoral votes. This decision is partly driven by the choice of state versus county level data.

One can consider electoral votes as a kind of log transformation. The effect of electorizing the popular vote is to pull the extreme values to the center. This significantly simplifies the designer's life. To wit, in the Post chart (shown nbelow), they have to apply a filter to highlight key counties, and you notice that those lines are so thick that all the other countries become barely visible.

## An example of focusing the chart on a message

##### Nov 01, 2016

Via Jimmy Atkinson on Twitter, I am alerted to this chart from the Wall Street Journal.

The title of the article is "Fiscal Constraints Await the Next President." The key message is that "the next president looks to inherit a particularly dismal set of fiscal circumstances." Josh Zumbrun, who tipped Jimmy about this chart on Twitter, said that it is worth spending time on.

I like the concept of the chart, which juxtaposes the economic condition that faced each president at inauguration, and how his performance measured against expectation, as represented by CBO predictions.

The top portion of the graphic did require significant time to digest:

A glance at the sidebar informs me that there are two scenarios being depicted, the CBO projections and the actual deficit-to-GDP ratios. Then I got confused on several fronts.

One can of course blame the reader (me) for mis-reading the chart but I think dataviz faces a "the reader is always right" situation -- although there can be multiple types of readers for a given graphic so maybe it should say "the readers are always right."

I kept lapsing into thinking that the bold lines (in red and blue) are actual values while the gray line/area represents the predictions. That's because in most financial charts, the actual numbers are in the foreground and the predictions act as background reference materials. But in this rendering, it's the opposite.

For a while, a battle was raging in my head. There are a few clues that the bold red/blue lines cannot represent actual values. For one thing, I don't recall Reagan as a surplus miracle worker. Also, some of the time periods overlap, and one assumes that the CBO issued one projection only at a given time. The Obama line also confused me as the headline led me to expect an ugly deficit but the blue line is rather shallow.

Then, I got even more confused by the units on the vertical axis. According to the sidebar, the metric is deficit-to-GDP ratio. The majority of the line live in the negative territory. Does the negative of the negative imply positive? Could the sharp upward turn of the Reagan line indicate massive deficit spending? Or maybe the axis should be relabelled surplus-to-GDP ratio?

***

As I proceeded to re-create this graphic, I noticed that some of the tick marks are misaligned. There are various inconsistencies related to the start of each projection, the duration of the projection, the matching between the boxes and the lines, etc. So the data in my version is just roughly accurate.

To me, this data provide a primary reference to how presidents perform on the surplus/deficit compared to expectations as established by the CBO projections.

I decided to only plot the actual surplus/deficit ratios for the duration of each president's tenure. The start of each projection line is the year in which the projection is made (as per the original). We can see the huge gap in every case. Either the CBO analysts are very bad at projections, or the presidents didn't do what they promised during the elections.

## The state of the art of interactive graphics

##### Mar 10, 2016

Scott Klein's team at Propublica published a worthy news application, called "Hell and High Water" (link) I took some time taking in the experience. It's a project that needs room to breathe.

The setting is Houston Texas, and the subject is what happens when the next big hurricane hits the region. The reference point was Hurricane Ike and Galveston in 2008.

This image shows the depth of flooding at the height of the disaster in 2008.

The app takes readers through multiple scenarios. This next image depicts what would happen (according to simulations) if something similar to Ike plus 15 percent stronger winds hits Galveston.

One can also speculate about what might happen if the so-called "Mid Bay" solution is implemented:

This solution is estimated to cost about \$3 billion.

***

I am drawn to this project because the designers liberally use some things I praised in my summer talk at the Data Meets Viz conference in Germany.

Here is an example of hover-overs used to annotate text. (My mouse is on the words "Nassau Bay" at the bottom of the paragraph. Much of the Bay would be submerged at the height of this scenario.)

The design has a keen awareness of foreground/background issues. The map uses sparse static labels, indicating the most important landmarks. All other labels are hidden unless the reader hovers over specific words in the text.

I think plotting population density would have been more impactful. With the current set of labels, the perspective is focused on business and institutional impact. I think there is a missed opportunity to highlight the human impact. This can be achieved by coding population density into the map colors. I believe the colors on the map currently represent terrain.

***

This is a successful interactive project. The technical feats are impressive (read more about them here). A lot of research went into the articles; huge amounts of details are included in the maps. A narrative flow was carefully constructed, and the linkage between the text and the graphics is among the best I've seen.

## Happy new year. Did you have a white Christmas?

##### Jan 04, 2016

Happy 2016.

I spent time with the family in California, wiping out any chance of a white Christmas, although I hear that the probability would have been miniscule even had I stayed.

I did come across a graphic that tried to drive the point home, via NOAA.

Unfortunately, this reminded me a little of the controversial Florida gun-deaths chart (see here):

In this graphic, the designer played with the up-is-bigger convention, drawing some loud dissent.

Begin with the question addressed by the NOAA graphic: which parts of the country has the highest likelihood of having a white Christmas? My first instinct is to look at the darkest regions, which ironically match the places with the smallest chance of snow.

Surely, the designer's idea is to play with white Christmas. But I am not liking the result.

***

Then, I happen upon an older version (2012) of this map, also done by NOAA. (See this Washington Post blog for example.)

There are a number of design choices that make this version more effective.

The use of an unrelated brown color to cordon off the bottom category (0-10%) is a great idea.

Similarly, the play of hue and shade allows readers to see the data at multiple levels, first at the top level of more likely, less likely, and not likely, and then at the more detailed level of 10 categories.

Finally, there is no whiteness inside the US boundary. The top category is the lightest shade of purple, not exactly white. In the 2015 version above, the white of the snowy regions is not differentiated from the white of the Great Lakes.

I am still not convinced about the inversion of the darker-is-larger convention though. How about you?

## Putting a final touch on Bloomberg's terrific chart of social movements

##### May 07, 2015

My friend Rhonda D. wins a prize for submitting a good chart. This is Bloomberg's take on the current Supreme Court case on gay marriage (link). Their designer places this movement in the context of prior social movements such as women's suffrage and inter-racial marriage.

Previously, I mentioned New York Times' coverage using "tile maps." While the Times places geography front and center, Bloomberg prefers to highlight the time scale. (In the bottom section of Bloomberg's presentation, they use tile maps as well.)

These are the little things I love about the graphic shown above:

• The very long time horizon really allows us to see our own lifetime as a small section of the history of the nation
• The gray upper envelope showing the size of the union is essential background data presented subtly
• The inclusion of "prohibition" representing a movement that failed (I wish they had included more examples of movements that do not succeed)
• The open circle and arrow indicators to differentiate between ongoing and settled issues

They should have let the movements finish by connecting the open circles to the upper envelope. Like this:

This makes the steepness of the lines jump out even more. In addition, it makes a distinction between the movements that succeeded and the movement that failed. (Prohibition was repealed in 1933. The line between 1920 and 1933 could be more granular if such data are available.)

## Designers fuss over little details and so should you

##### Mar 25, 2015

Those who attended my dataviz talks have seen a version of the following chart that showed up yesterday on New York Times (link):

This chart shows the fluctuation in Arctic sea ice volume over time.

The dataset is a simple time series but contains a bit of complexity. There are several ways to display this data that helps readers understand the complex structure. This particular chart should be read at two levels: there is a seasonal pattern that is illustrated by the dotted curve, and then there are annual fluctuations around that average seasonal pattern. Each year's curve is off from the average in one way or another.

The 2015 line (black) is hugging the bottom of the envelope of curves, which means the ice volume is at a historic low.

Meanwhile the lines for 2010-2014 (blue) all trace near the bottom of the historic collection of curves.

***

There are several nice touches on this graphic, such as the ample annotation describing interesting features of the data, the smart use of foreground/background to make comparisons, and the use of countries and states (note the vertical axis labels) to bring alive the measure of coverage volume.

Also, this post talks about finding real-life anchors to help readers judge size data.

My collection of posts about New York Times graphics.

PS. As Mike S. pointed out to me on Twitter, the measure is "ice cover", not ice volume so I edited the wording above. The language here is tricky because we don't usually talk about the "cover" of a country or state so I am using "coverage". The term "surface area" also makes more sense for describing ice than a country.

## Cloudy and red

##### Dec 22, 2014

Note: I'm traveling during the holidays so updates will be infrequent.

Reader Daniel L. pointed me to a blog post discussing the following weather map:

The author claimed that many readers misinterpreted the red color as meaning high temperatures when he intended to show higher-than-normal temperatures. In other words, the readers did not recognize a relative scale is in play.

That is a minor issue that can be fixed by placing a label on the map.

There are several more irritants, starting with the abundance of what Ed Tufte calls chartjunk. The county boundaries do not serve a purpose, nor is it necessary to place so many place names. State boundaries too are  too imposing. The legend fails to explain what the patch of green in Florida means.

The article itself links to a different view of this data on a newly launched site called Climate Prediction Center, by the National Oceanic and Atmospheric Administration (link). Here is a screenshot of the continental U.S.

This chart is the other extreme, bordering on too simple.

I'd suggest adding a little bit of interactivity to this chart, such as:

• Hiding the state boundaries and showing them on hover only
• Selectively print the names of major cities to help readers orient themselves
• Selectively print the names of larger cities around the color boundaries
• Using a different background map that focuses on the U.S. rather than the entire North American continent

This is a Type V chart.

## A great visual of complicated schedules

##### Jun 16, 2014

Reader Joe D. tipped me about a nice visualization project by a pair of grad students at WPI (link). They displayed data about the Boston subway system (i.e. the T).

The project has many components, one of which is the visualization of the location of every train in the Boston T system on a given day. This results in a very tall chart, the top of which I clipped:

I recall that Tufte praised this type of chart in one of his books. It is indeed an exquisite design, attributed to Marey. It provides data on both time and space dimensions in a compact manner. The slope of each line is positively correlated with the velocity of the train (I use the word correlated because the distances between stations are not constant as portrayed in this chart). The authors acknowledge the influence of Tufte in their credits, and I recognize a couple of signatures:

• For once, I like how they hide the names of the intermediate stations along each line while retaining the names of the key stations. Too often, modern charts banish all labels to hover-overs, which is a practice I dislike. When you move the mouse horizontally across the chart, you will see the names of the unnamed stations.
• The text annotations on the right column are crucial to generating interest in this tall, busy chart. Without those hints, readers may get confused and lost in the tapestry of schedules. If you scroll to the middle, you find an instance of train delay caused by a disabled train. Even with the hints, I find that it takes time to comprehend what the notes are saying. This is definitely a chart that rewards patience.

Clicking on a particular schedule highlights that train, pushing all the other lines into the background. The side panel provides a different visual of the same data, using a schematic subway map.

Notice that my mouse is hovering over the 6:11 am moment (represented by the horizontal guide on the right side). This generates a snapshot of the entire T system shown on the left. This map shows the momentary location of every train in the system at 6:11 am. The circled dot is the particular Red Line train I have clicked on before.

This is a master class in linking multiple charts and using interactivity wisely.

***

You may feel that the chart using the subway map is more intuitive and much easier to comprehend. It also becomes very attractive when the dots (i.e., trains) are animated and shown to move through the system. That is the image that project designers have blessed with the top position of their Github page.

However, the image above allows us to  see why the Marey diagram is the far superior representation of the data.

What are some of the questions you might want to answer with this dataset? (The Q of our Trifecta Checkup)

Perhaps figure out which trains were behind schedule on a given day. We can define behind-schedule as slower than the average train on the same route.

It is impossible to figure this out on the subway map. The static version presents a snapshot while the dynamic version has  moving dots, from which readers are challenged to estimate their velocities. The Marey diagram shows all of the other schedules, making it easier to find the late trains.

Another question you might ask is how a delay in one train propagates to other trains. Again, the subway map doesn't show this at all but the Marey diagram does - although here one can nitpick and say even the Marey diagram suffers from overcrowding.

***

On that last question, the project designers offer up an alternative Marey. Think of this as an indiced view. Each trip is indiced to its starting point. The following setting shows the morning rush hour compared to the rest of the day:

I think they can utilize this display better if they did not show every single schedule but show the hourly average. Instead of letting readers play with the time scale, they should pre-compute the periods that are the most interesting, which according to the text, are the morning rush, afternoon rush, midday lull and evening lull.

The trouble with showing every line is that the density of lines is affected by the frequency of trains. The rush hours have more trains, causing the lines to be denser. The density gradient competes with the steepness of the lines for our attention, and completely overwhelms it.

***

There really is a lot to savor in this project. You should definitely spend some time reviewing it. Click here.

## Two good maps, considered part 2

##### Dec 30, 2013

This is a continuation of my previous post on the map of the age of Brooklyn's buildings, in which I suggested that aggregating the data would bring out the geographical patterns better.

For its map illustrating the pattern of insurance coverage in several large cities across America, the New York Times team produced two versions, one using dots to plot the raw data (at the finest level, each dot represents 40 residents) and another showing aggregate data to the level of Census tracts.

We can therefore compare the two views side-by-side.

The structure of this data is similar to that of the Brooklyn map. Where Rhiel has age of buildings as the third dimension, the NYT has the insurance status of people living in Census tracts. (Given that the Census does not disclose individual responses, we know that the data is really tract-level. The "persons" being depicted can be thought of as simulated.) The NYT data poses a greater challange because it is categorical. Each "person" has one of four statuses: "uninsured", "public insurance", "private insurance" and "both public and private insurance". The last category is primarily due to aggregation to the tract level. By contrast, the Brooklyn data is "continuous" (ordinal, to be specific) in the year of construction.

The aggregated chart at the bottom speaks to me much more loudly. What it gives up in granularity, both at the geographical level and at the metric level, it gains in clarity and readability. The dots on the top chart end up conveying mostly information about population density across Census tracts, which distracts readers from taking in the spatial pattern of the uninsured. The chart in the bottom aggregates the data to the level of a tract. Also, instead of showing all four levels of insuredness, the chart in the bottom concentrates its energy on showing the proportion of uninsured.

In short, the chart that uses fewer elements (areas rather than dots), fewer colors, fewer individual data points ends up answering the question of "mapping uninsured Americans" more effectively. (It is a common misunderstanding that aggregation throws away data -- in fact, aggregation consumes the data.)

***

When designers choose to plot raw data, they often find a need to compensate for its weakness of losing the signal in the noise. One of the strategies is to produce a hover-over effect that shows aggregated statistics, like this:

Notice the connection between this and my previous comment. What the aggregated map displays are two elements of the hover-over: the boundary of the Census tract, and the first statistic (the proportion of uninsured).

In addition to the hassle of having to hover over different tracts asynchronously, the reader also loses the ability to interpret the statistics. For example, is the proportion of uninsured (21.4%) a good or bad number? The reader can't tell unless he or she has an understanding of the full range of possibilities. In the other chart, this task has been performed by the designer when constructing the legend:

This trade-off between relative and absolute metrics is one of the key decisions designers have to make all the time. Relative metrics also have problems. For instance, on the bottom chart, the reader loses the understanding of the relative population density between different Census tracts.

A similar design problem faced by Rhiel in the Brooklyn chart is whether to use the year of construction (e.g. 2003) as the metric or the age of buildings (10 years old). Rhiel chose the former while some other designer would have selected the latter.

***

Again, thanks for reading, and see you next year!