Sankey diagrams are handy ways to visualise material or energy flows through usage and time. They are excellent for displaying energy source and usage, for example the UK government publishes a Sankey diagram of UK energy each year (pdf).

Perhaps the most famous example is Charles Joseph Minard's remarkable visual showing Napoleon's invasion of and retreat from Russia in the Winter of 1812–13. In that chilling example the thickness of the lines represent the remaining size of Napoleon's army.

I learned about Sankey diagrams from Edward Tufte but perhaps people see them most commonly today in Google Analytics showing the different paths visitors take on a website before leaving.

Sankey diagram

The data prison is the default table where the bars of the cells crowd out your data with non-data-ink and lock your data into a prison.

When data is locked into cells, their relationships with other data are harder to see, and the reader has to work harder to learn from your table.

When making a table of data, consider if, by adjusting spacing and alignment, you can make the columns or rows clear enough as they are without the prison bars. And look for opportunities to remove the visual noise to let your data and the relationships between them shine out.

The data prison is a concept from Edward Tufte. Check out the beautiful Envisioning Information

The data prison

There’s a famous photo series by Eadweard Muybridge that shows, unequivocally, that while galloping all four of a horse’s legs leave the ground. I’d always heard that’s what they trying to find out at the time, but from what I’ve read it was more a question of at what points do a horse’s legs leave the ground. The photos show the somewhat surprising state of leaving the ground while the horse’s legs are tucked, not when they are outstretched. It’s a lovely example of what Edward Tufte calls small multiples.

Do horses legs leave the ground at a gallop?

I often find myself reflecting on what ought to be an improvement to the caveman-esque communication method, which is the car horn.

My theory generally goes that the vast majority of use of a car horn, in the UK at least, is not for its intended of use of signalling to others to watch out. Instead it probably has most use in telling people they're idiots, perhaps for pulling out in front of you. Next, letting the person in front know that the light has turned green, followed by letting your friends know you're waiting outside or just leaving. And, lastly, to let people know to watch out.

But it’s harder than it seems, I'd guess, to make something that supports helpful behaviour provides safety and avoids lawsuits. Surely can’t be that hard though…

Use of the car horn

Data graphics can lie in many ways, but the most common, I expect, is the error of using area or volume objects to represent one-dimensional data.

More data visualisation principles from Edward Tufte.

Watch for the lie factor

Principles from Edward Tufte. Remove chart junk. Erase redundant and non-data-ink. Above all else show the data.

Of course the present infographic trend laughs in the face of these principles in the interests of trying to encourage people to actually look at the data in the first place. But, assuming you actually want people to seriously infer some meaning from the data, these are not bad principles to follow when constructing your data graphics. Some basic Excel templates could do with a clean up for example.

Maximise data-ink

It was my goal to explain one thing a day for a year. With this one I cross half-way.

Sincerely, thanks everyone for following. Ideas, suggestions, and motivation always very much appreciated.

Sketchplanation statistics

If a baby wore 2 reusable nappies per day, that’s nearly 1500 nappies saved from landfill by the time a child is 2 years old. If every baby born in the UK did this, that’s 2.5 Big Ben’s worth saved from landfill.

Save some landfill with reusable nappies/diapers

Getting beyond the getting stuck taught me by Dev Patnaik. The first 50 are the same as everyone else’s via Emily Ford.

Infographics sketches