Visualizing a Campus Carbon Footprint
How do you show the relative contribution of 300 buildings to a campus’s carbon footprint? You might think pie chart, but then you’d have 300 slices and enough labels to make your head spin. Why not try a Tree Map, instead?
A tree map represents each category as a box whose size corresponds to the measurement in question. The boxes can be grouped and arranged into categories, so you can get a sense of how each item contributes to its class, and how each class adds up to the whole.
I made this tree map for the University of North Carolina at Chapel Hill’s carbon inventory, and it shows the carbon footprint of every building on campus. You can quickly see that laboratory buildings are by far the largest energy users. Individual buildings, like Thurston-Bowles, have a larger carbon footprint than all the dining halls combined! By examining the data in this way, you can begin to prioritize your energy efficiency strategies. For example, you might choose to do a retro-commissioning project in a single lab, rather than doing projects in 10-15 residence halls with smaller gains per building.
Tree maps are not perfect, though, and you should keep their limitations in mind when you use them. First, they rely on different areas to convey information, and unfortunately, the human visual system is not great at comparing areas. This is further confused by the fact that all the boxes have different shapes. A perfect square and an elongated rectangle may have the exact same area, but they look very different to the viewer. So if you want to show relative proportions, rather than exact values, a tree map might work for you.
This particular tree map is practically famous, as it found its way into an article from Intelligent Enterprise. Check it out, as well as, other examples of useful visualization techniques at their website. Thanks to Arati at SAS for pointing out the article!
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