I was visiting my very good friend Turf Miller in Chicago when we got into a wonderful discussion. We were talking about how so much of geographic “bucketing” on the web for various business purposes was done by zip code and how arbitrary that seemed. We discussed how using latitude and longitude bounding boxes might be a better system for bucketing location.
Here is a quick and dirty comparison of current zip code boundaries vs. using latitude and longitude to define a geographic area to test out our idea.
The map below shows the 55117 zip code area in green. As you can see, it is a very irregular shape that is probably optimized for physical delivery of mail, but that is really just speculation.
The zip code ‘55117’ has only 5 numbers for a person to remember. This seems like a relatively moderate cognitive load and we would like to try to match this level of complexity with any substitute alternate system.
Our first attempt is to use a bounding box with six total numbers to remember (shown in red below). The idea is that you could specify any address within a bounding box comprised of a concatenation of the latitude (three significant digits) and longitude numbers (another three significant digits) and get a geographical area.
The bounding box for our geographic construct (actually a trapezoid since the lines of longitude are not parallel) is ‘449931’ in the southeast to ‘450932’ in the northwest. The ‘499931’ signifies 44.9 to 45.0 latitude (449) and -93.1 to -93.2 longitude (931). In each case we are selecting the lower bound of a range of one-tenth of one degree of arc to identify the bounding box.
The idea here is that five numbers for a zip code and six numbers for this new system are roughly equivalent and easy to memorize. But as you can see in the map, using just six numbers gets us an area that is much larger than our test zip code. To get a comparable area to the 55117 zip code, we actually need to go to eight digits in the latitude and longitude scheme as shown in blue, below. This may still be a reasonable cognitive load, but it is definitely larger than 5 digits.
Of course, we have just pulled out a single zip code example and various zip codes across the U.S. may be larger or smaller since we haven’t really considered the factors that go into zip code definitions.