Time travel


One of my scientific heroes and seminal teachers is Professor Frank Kelly at Cambridge.  What a pleasant surprise to see his involvement in a data visualization project.  To cite his wise words:

The travel-time maps are more than just pretty to look at; they also demonstrate an innovative way to use and present existing data. We are entering a world where we have access to vast quantities of data, and ways of turning that data into information, often involving clever ideas about visualisation, are becoming more and more important in science, government and our daily lives.

The little black dot near the center of the map indicates the Mathematics building at Cambridge.  The contours (vaguely visible at our scale) represent intervals of 10 minutes by public transportation away from the black dot.  Any colored dot on the map refers to the time at which a traveller must leave in order to get to the Math building by 9 am, taking into account traffic situation, time of day, and decisions.  The hope of such maps is to help commuters (by public transit) plan their travel.

Professor Kelly has a very nice write-up on the intricacy of generating the data for such a map, which includes techniques of sampling, smoothing, extrapolation and so on.  It is rare that we get insights into the chart-making process.  He also carries a larger version of the travel-time map.

A similar article can be found at Plus magazine.

In Praise of the Bumps Chart III

Many authors have exposed and harangued statistical liars (e.g. "How to Lie with Statistics").  Likewise, I rant here once in a while.  However, not every distortion of reality is unwarranted.  Sometimes, distorted data actually bring out key insights.  I go back to the Bumps chart to illustrate this point.

Bumps_exIn a previous post, I remarked that the vertical axis can represent either ranking or boat locations along the river.  Reading the chart from left to right as if from start to finish of the race, we suggest the right-side list displays the ending ranks or ending locations of boats.

On second thought, the right-side list cannot give us the ending locations!  Physically, the boats would have moved downstream so the entire list needs to be shifted downwards to be precise.  But we feel comfortable with the current arrangement: this is a distortion of reality which does not affect our reading ability.  Indeed, it enhances our ability to see into the data because now a horizontal line means no change in ranks.

If one is very particular, then one should interpret the right side as next year's starting locations rather than the current year's ending locations.  Then all is well.

In many situations, reducing continuous data to ranks introduces significant distortion and is thus not advisable.  For the Bumps chart, because the Bumps rules require that all boats start next year the same distance apart, in essence wiping out the year-end separations, the form perfectly fits the function!  This distortion removed information not needed to grasp the key point of the chart, so no harm done!

As a side note -- Tim Granger has produced a side-by-side Bumps chart, even more marvellous than the single-period chart.  Redo_bumps_all_2In my junkart version, I removed the horizontal line segments linking one year to the next.  These line segments contain no data; besides, based on the discussion above, each right vertical axis should be interpreted as next year's starting locations rather than this year's ending locations, so these line segments are unnecessary.

PS. In case you're wondering, Tim colored some lines red to indicate boats that managed to bump up each of the four days in a specific year.  These teams win an award called the "blades".  If the purpose of the chart is to identify the rise and fall of boat club dynasties then we would have colored the trajectory of Pembroke (6) and Queens (19), for example.

In Praise of the Bumps Chart II

Bumpschart2005On the left is my beloved Bumps chart (Cambridge 2005 May Bumps). It has a perfect union of function and form.  Here are some salient features:

  • The horizontal axis records time: the first and second columns of text display the starting and ending orders of the college boats.  The zigzagging lines delineate each boat's movement over the four days of the race.
  • The vertical axis serves dual functions: it both gives the current ranking and maps to the physical location of the boats along the river.
  • What we care about is the movement of a boat over the four days; what we really care about are boats that have moved a lot, either up or down. The chart manages to highlight precisely what we want to see: the larger the movement, the steeper the line, the more attention it gets from our eyes.
  • Focusing on #10 and #11: the criss-crossing lines tell a rich story of tit-for-tat over four days, in which the boats exchanged bumps during the first three days, with the Jesus boat leading after day 4.
  • The story at #1 (Caius) was altogether different: as "Head of the Cam", this strong boat eluded the chasing fleet all four days.
  • My alma mater started and ended at #3 (Trinity Hall)

A truly spectacular chart can be produced by placing all the historical 4-day charts side-by-side, painting a rich history of the rise and fall of different boat clubs over decades.  If anyone has seen such a chart, please send it my way!


In Praise of the Bumps Chart I

In my opinion, the Bumps chart takes the crown for perfect alignment of function and form. In this post, I describe the Bumps boat race and in the next post, I will explain why I like the Bumps chart so very much.

Unlike American colleges, where athletics claim a prominent role and where athletes achieve iconic status, at British universities pretty much the only sport that matters is rowing (called crew in the U.S.).  In particular, the annual Boat Race between Cambridge and Oxford can be compared to the Game between Harvard and Yale. Now, Cambridge and Oxford both consist of more than a dozen colleges, which are autonomous academic and residential units.  Each college has their own boat club and their boaties (rowers) face off at races known as "Bumps".

Ccat_bumps_2The Boat Race is a standard side-by-side race: the first boat to cross the finish line wins.  By contrast, at the Bumps, the competing boats start from a single line; each boat chases the boat ahead by "bumping" or touching before it gets "bumped" by the boat behind.  When a bump occurs, both boats exit the race.

The Bumps happen over four days, with one race on each day.  Thus, after four days, normally a boat can move up or down by up to four slots.   On rare occasions, a boat can "over-bump": this happens if the two boats in front bump, and the said boat then catches up with the boat that has started three slots in front.  Triple over-bumping has also occurred, which means a boat has moved up five slots in one day.

The starting order of one year is the ending order of the previous year, ever since the 1820s (at Cambridge).

Reference: First and Third Boat Club, Trinity College, University of Cambridge