It’s a situation all too familiar—you’re working on a mapping project. You may be looking to highlight population, median income, or whatever statistic hits the issue of the day. Someone suggests a zip code map. Great idea!
Far from being a series of neat, polygons with clearly defined borders, you get a tangled octopus of overlapping areas, non-contiguous areas, and some areas completely engulfed by another, larger area. It makes your presentation more confusing, and now you’re wondering if you wasted your time in getting these printed up.
You’re not alone in being completely confounded by the ugliness of zip code maps.
It can feel frustrating to be looking at beautifully rendered county lines or school districts, only to turn the page onto a perplexing mess. In fact, one of the most common initial reactions to a zip code map is probably “What am I looking at here?” The main reason for the striking difference is that while municipalities might be keen on keeping borders logical, zip codes were not designed with municipalities in mind. They were designed with mail carriers in mind.
For instance, let’s take a look at Boston. Boston is an old city, and a port city, so the USPS had a few challenges to work with. Take a look at the picture below. Notice how some zip codes appear to cover areas of open water? See how others appear to jut sharply into their neighbors, before turning back the way they came?
When Postal Inspector Robert Moon first proposed zip codes in 1944, he was not thinking about how they would look on a map. He was hoping they would add some efficiency to an increasingly overwhelmed mail delivery system. So rather than laying out areas “as the crow flies,” the USPS had to lay out areas “as the mail carrier hoofs it.” That’s how you get portions of zip code areas meandering off in strange directions, stopping and starting again, and winding around themselves. It was built for people following already-established roads and navigating communities.
Cities can be enough of a bear to map out by zip code, but that’s still nothing compared to a rural zip code map. Remember that these are meant to aid in physical mail delivery, and therefore when you have hundreds of acres — sometimes miles — between neighbors, attempting to draw a polygon around a rural zip code is useless. You’re more likely to see a zip code area that follows a few scattered roads around for miles, before finally hitting a more populated area.
In some cases, there are parts of the map that seemingly have no zip code at all. These are usually found out in very rural, or totally undeveloped areas. Sometimes, these swaths of (mostly) empty land are assigned either a “rural route” (which is different from a zip code), or have no mail delivery at all. Any brave soul willing to live out in the middle of nowhere has to make their own way to the nearest post office in order to collect their mail.
Then you have the mysterious Zip+4 system, making things just a little more messy. This is a system developed in 1983 meant to help pinpoint large apartment complexes, office buildings, or PO Boxes. One large office park could potentially add thousands of new mailing addresses into the mix, and the zip+4 numbers are there to help letter carriers sort through the larger mail volume more accurately.
This is the part where you are probably wondering “What’s the harm in just offering up an approximate zip code area, and evening out the lines a little?” I would counter that by asking you if aesthetics are really more important than hard data (hint: they’re not).
Any zip code map that purports to show neatly outlined, interlocking zip code “areas” or “polygons” is, at best, misleading. In some special circumstances like a large city, or the aforementioned rural roads, a “fudged” zip code map could actually be wildly inaccurate. You’re not doing your clients any favors by giving them incorrect data. They can handle a few weird lines on a map if it means they’ll get valuable information out of it.
When you’re rendering maps, you’re doing so with the intention of planning something. Whether that happens to be the best route to a vacation home, or the best location for a new startup business, the bottom line is that you need it to be accurate. If you were following a map that has wishy-washy information, you might not know if you’re 10 miles, or 50 miles to the nearest gas station. That’s a pretty crucial difference, especially if you’re trying to limp your car ahead before getting stranded.
Likewise, maps meant to present spatial data need to be precise, if they are going to be useful. Does the zip code end on 1st street, or on 5th street? For someone referencing that map it might mean the difference between their bills getting paid on time, or getting hit with a late fee. That person isn’t going to thank you for smoothing out the edges on the map you made. They’ll thank you for getting it right.
The invention of zip codes doesn’t mark the first time a map has been played around with. The Mercator Projection is the name given to many world maps sitting in classrooms. In an attempt to account for the distortion that happens when drawing a spherical object on flat paper, many countries were drawn inaccurately. And because we value accuracy in our maps, there is some debate going on right now about how our world maps should actually look. See the illustration below for the drastic difference.
And anyway, there can be beauty in the oddness of zip codes, assuming they’re presented right. We just began a new mapping project using Mapbox. Thanks to its amazing capabilities, we are now able to create beautiful maps — jagged zip code lines and all. You can wow your clients and partners too with these accurate, and fantastically rendered maps. The right program will help you make sense of the otherwise quirky boundaries of zip codes.