Monday, July 21, 2008

Geographic Charts

proportional (prə-pōr'shə-nəl) adj.
  1. properly related in size, degree, or other measurable characteristics
Visualization is supposed to make it easier to understand data, not mislead the user.

It seems like a requirement that all BI software provide the ability to display data on a map. I just read that Tableau introduced this in their latest release, but most other vendors have provided this ability for a couple years (including my employer, InetSoft).

Maps have a few things going for them. They are familiar ways of displaying geopolitical entities (States, Countries, etc.), and they represent spatial data well.

The issue is that maps are often used to display data, like sales, by filling the interior of the region with a highlight color. Why is this a problem? Because the size and shape of a region directly impacts its visual notability, but has little correlation to population, market size, and general importance.

Consider low sales in Massachusetts and high sales in Montana. A larger portion of the US map would look good, but this belies the truth. I am reminded of a model that shows what a human body would look like if each part was in proportion to the area of the brain involved in its sensory perception.

I am not as much a stickler as Stephen Few when it comes to visual display. I am in favor of nice looking graphs, but not at the expense of conveying accurate information.

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