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Some “Camel Curves” for World Camel Day

Sometimes, how you present the information is more important than the information you present.

When I started doing large-scale parking demand analyses as the Great Recession lifted, the “industry standard” was to graph parking demand using bar charts. Each hour that demand is observed is plotted on the horizontal axis, and for each hour a bar is plotted; the height of that bar is proportional to the percentage of observed spaces that were occupied at that hour. It’s a bit of a mouthful to explain, and a bit of an eyeful to observe. Take this example, produced by Kittelson and Associates for a 2008 study in Central Portland:

Yuck! Several things are suboptimal about that presentation (aside from the artifacts of scanning, of course), the most obvious of which is that it ignores Edward Tufte’s cardinal rule to always craft your infographic so as to use as little ink as possible. But even more than this, you can look at charts like this over and over again and never notice a pattern among the noise. The presentation as a bar chart doesn’t really allow for one of the human brain’s best assets—it’s pattern recognition super-power—to take over.

We can solve both of these inefficiencies simply by graphing the data with a humble little line instead:

Even though the pattern between the old bar chart and new line graph are relatively similar, it’s a lot easier to spot the basic trends and understand what’s going on in the bottom one, isn’t it? In particular, you can see that there are two peaks, with one occurring in the early afternoon and a second one in the early evening. What’s interesting is that, no matter where we looked in Central Portland, we saw some manifestation of this pattern. For example, here’s one from the Pearl District:

Since the pattern popped up so often, it needed a name. Hence, Camel Curves:

While the “camel reveal” is always good for laughs when talking about an otherwise dry topic, I think it actually provides a useful framework. The number of humps—are we talking about a Bactrian or a Dromedary camel?—size of the humps, and depth of the valley between can be used to divine a lot of information about what’s driving parking demand. For instance, you can see that the Pearl District’s two-humped camel is largely similar to downtown Portland’s, except that rightmost hump on the Pearl District’s camel rises up a bit higher. This tells us that it’s a relatively similar mix of uses driving demand in both districts, but the Pearl’s demand is more driven by evening-heavy uses like dining and shopping than downtown.

Eventually, we came to realize that the two-humped pattern we saw throughout downtown Portland was virtually inevitable in dense, mixed use districts where multiple types of land uses drive parking demand. For instance, here’s one we spotted in Charlotte. It’s got plenty of similarities to downtown Portland and the Pearl, which again owe to similar land use patterns with subtle differences. In Charlotte, the sharp peaks result from relatively more demand being driven by restaurant and retail uses than here in Portland, as a larger stock of off-street parking in the Queen City absorbs a greater share of residential and commuter demand:

Of course, when we start to get away from mixed-use areas, we start to see single-humped camels. Take a look at Cannon Beach, Oregon, where the big, beautiful ocean is the biggest driver of demand. The single peak happens in mid-afternoon, when beach demand is the highest, although the restaurants and entertainment in the tourist town ensure that the midday peak is not terribly pronounced:

 

It’s rather kitschy, but I have yet to see a parking demand curve that deviates too far from the shape of a camel’s back. Many thanks to my partner Sarah Davis for humoring be and drawing all of these camels over my parking demand curves, and Happy World Camel Day!

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