Update: Smee correctly points out that while a Histogram and a Bar Chart are superficially similar, they are not really similar at all. I am properly chastised and have updated the post appropriately.

Look! An excuse to embed a Hulu video on the blog – w00t! (If you go full screen on the video, you can see the element under discussion.)

So, Hulu (a favorite of mine) rolled out a new version of their online video player. Kudos to the team! Generally speaking I like the new player – it’s cleaner than previous (not sure how they made it more sparing than it was before) and the dynamic bit rate is pretty damn awesome but there are a few things that I don’t like (the new loading spinner, the inauthentic-feeling "is this ad relevant to you?" and this new fangled thing they call a "Heat Map".

Here’s what wikipedia has to say about heat maps:

A heat map is a graphical representation of data where the values taken by a variable in a two-dimensional map are represented as colors. A very similar presentation form is a tree map. The term is also used to mean its thematic application as a choropleth map.

Not a bad definition, especially for my purposes here. Two aspects of the definition are key here:

1. “…values taken by a variable in a two-dimensional map…”
2. “…are represented as colors.”

So the basic structure of the map is two dimensional – perhaps a Cartesian coordinate system and the values of the variable are represented as a color. What does something like that look like? Here is an example:

We have a basic x (horizontal) – y (vertical) coordinate system and then blobs of color represent where users spend the most attention (as measured by eye-tracking). The deep, red colors indicate high-attention areas while the cooler, more shallow colors (green) represent less attention.

Here’s what Hulu is calling a heat map:

Wait … what? Hulu says this is a heat map? Unfortunately, it only has one dimension (time) for it’s variable (Popularity) and it is monochromatic – a stepped gray scale. It has failed all the tests contained in the heat map definition above. Oh, and its a Bar Chart.

Going back to our favorite source of definitions, Wikipedia has this to say about Histograms

A bar chart or bar graph is a chart with rectangular bars with lengths proportional to the values that they represent. The bars can also be plotted horizontally.

Bar charts are used for plotting discrete (or ‘discontinuous’) data i.e. data which has discrete values and is not continuous. Some examples of discontinuous data include ‘shoe size’ or ‘eye colour’, for which you would use a bar chart. In contrast, some examples of continuous data would be ‘height’ or ‘weight’. A bar chart is very useful if you are trying to record certain information whether it is continuous or not continuous data.

In this case, we are probably looking at a simplified Histogram — a bar chart — where the bar height equals the frequency of the interval as opposed to the area as described above.

Here’s an example of a bar chart:

This looks a lot more like what Hulu is doing in their so-called heat map.

So why call it a heat map when its clearly a bar chart?

If its a naming thing, why not call it the Popularity Curve? I get that bar chart is business-boring. But, “heat map” is an established visualization concept with concrete rules and its nothing like a bar chart.

Now, I’m not saying that the underlying concept here is bad – I think it may be quite interesting (more on that later).

All I’m saying is why call something that it isn’t when on the one hand that misnomer already exists as its own unique concept and on the other hand the original thing is probably the best solution anyway? This isn’t a Shakespearean issue (calling a rose by any other name … I’m paraphrasing here). A heat map is not a bar chart and no amount of wishing will make it so. They are designed to solve different problems.

So, Hulu, let’s call things what they are shall we? What you’ve got there is a bar chart and no amount of wishing will make it a heat map. The bar chart is a good solution – go with it and spend a little more time coming up with a better name for the product than a misapplied name for a completely different visualization technique.

So what’s the purpose of this thing anyway? It’s seemingly obvious, show users where the most attention is paid in a particular show. Straightforward.

But, why?

Content discovery.

If you’ve never seen Glee before, this tool will (hopefully) show you where all the good bits are – according to all the other viewers. Or, if you missed Saturday Night Live with Betty White over the weekend and need to be prepared to talk about it at the water cooler on Monday then the popularity curve will show you all the skits that folks found funny and maybe you can save some time by only watching those sketches instead of the whole episode. This encourages both new and regular viewers to watch more content and to find new content that they enjoy. Pretty cool right?

So what should Hulu call this utility (assuming that you agree that “heat map” is the wrong name for it)?

Tags: heat-map, histogram, hulu

This entry was posted on Thursday, May 13th, 2010 at 10:35 pm and is filed under visualization. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.