Yesterday the BBC published an article about the success of the United Kingdom’s creative industry especially given the not-so-successful economy of the last few years. Unfortunately, the article included the tree map below.
The problems are a few. First, a tree map is usually looking at two variables. One is encoded through the size of the block and the other often its colour. Here, colour means nothing. So you are instead looking at only the size of the blocks. Basically, the same type of information that would be clearer to differentiate if this were a bar chart.
Second, a tree map has a hierarchy of placement. In other words, even if you cannot tell how much larger one block is from another—we all know we are not so great at comparing areas—you know which block is larger than the other by their arrangement in the map. Here we see no such hierarchy. The smallest block follows the largest block, which itself follows three other blocks.
Now that arrangement would be acceptable if the tree map were nested. That is to say if the different industries were grouped within like industries. Because then you would order those nested blocks. But that is also something not happening here.
All in all, this would have been a lot more effective of a chart if it had simply been made into a bar chart.
Credit for the piece goes to the BBC graphics department.