An image published in a book or article can be viewed and analyzed at the reader's leisure, whereas a projected image in a classroom lecture or other presentation venue is usually only visible to a viewer in the class or audience for seconds or minutes. Are there any aspects of image design that apply to both these situations, or are they two distinct problems with very different solutions? Thanks.

Mr Tufte,

I sometimes have issues with default colours in graphs being too similar to each other to be easily differentiated.

Given a number n (assume between 5 and 25 or so) is there an algorithm to generate a set of RGB colours that are most differentiatable from each other to the human eye? I believe such an algorithm may need to take into account human biology.

I firmly believe research on this subject must have been done and yet I can't find anything, not even canned lists of 12 optimally differentiatable colours for instance.

Have you come across this problem in your travels?

Thanks in advance,
Paul

Now that it has become so easy to generate coloured pictures with computers, this sensible advice is more and more widely ignored. At the moment I am assessing a doctoral thesis in which the author has a graph with 1600 spots colour-coded for degrees of heterosis from 0 to more than 200%. (Heterosis is a genetic measure of the extent to which a child deviates from the average for the two parents). It's not a bad graph from the point of view of information density, but unfortunately the two darkest colours (out of five) refer to "0" and "more than 200%", with three fainter colours used for the intermediate degrees (one of them so faint as to be almost invisible). As a result it is very difficult for the eye to pick out much in the way of a pattern. With shades of grey it could have been so much better, and the author could have distinguished between more than five levels in a way that would have been intuitively clear.

In terms of representing scale, one of the most powerful mechanisms I find useful is to use examples people can grasp in meaningful terms. In the Boston seminar, ET uses the "amount of data in a phone book" as one of those conceptual hooks. I think I caught him say that a typical phone book contains 38,000 characters. Did I hear that right?

And, while I raised the topic, do you have other credible examples of this kind of metric? For example, I'm trying to explain to people how much a terabyte of data is; the best example I have found so far is that the entire Library of Contents is estimated to be about 10 terabytes of data. That's a good way to make that staggering number real.

And, today, I heard another one, that there are about a billion bags checked for air travel, world wide, in a year.

I'm curious if anyone else has some favorite ways of representing scale in concrete, understandable terms.

We produce many tables and lists in our publications group, in print, presentations, and web pages. There is a growing trend toward using "zebra tables", alternating bands of background color for every other row.

While this can look graphically cute when viewed at a distance, I find my eye jumps to all the even (or odd) rows when scanning for information, so that I must constantly back up and rescan.

Is my observation backed by any other evidence, or am I just a whiner? I would appreciate a reference to a good discussion on design of tabular information.

Thanks,
Bruce Hensley

My understanding is that rounding to two digits makes numbers easier to read, use and recall later. Certainly I find that to be the case. Obviously there are numbers that can't be rounded — bookkeepers have to account for every penny/cent, etc. But for general management purposes, marketing, decision-making, rounding can make data more lucid.

The original reference I have on rounding to two digits for clarity is "Washburne, 1927". ( I don't know who Washburne was or what he/she actually proved or asserted.) Does anyone know of relevant research about rounding improving readability?