Explore these chaotic maps that link every postal code together in ascending numerical order. It works for other countries, too.

The Zone Improvement Plan, or ZIP code system as we know it today, was robustly rolled out in 1963 with the purpose of modernizing the mail-sorting process. But this updated postal zoning system ended up doing a lot more. ZIP codes have led to fine-grained information about American neighborhoods, including how rich, poor, and unequal they are, who lives there, and how the place is changing. Here’s how the U.S.P.S. Inspector General put it in a 2013 report called “The Untold Story of the ZIP Code”:

Today, the ZIP Code is much more than a tool for moving mail efficiently, and its positive spillover effects are enormously beneficial to society.

But data viz expert Robert Kosara wanted to go beyond individual ZIP code. He wondered if examining how they were spread out would reveal interesting patterns. To satisfy his curiosity, he created this interactive “Scribble Map” by connecting each dot representing each U.S. ZIP code in ascending order. Here’s what Kosara tells CityLab is the key takeaway from his visualization, via email:

Perhaps the main thing is to appreciate the structure in ZIP codes. Most people probably never think about where they come from or why there are certain numbers in certain places. But they're all planned and structured, and surprisingly interesting to look at.

He’s right. The U.S. map of connected codes is a jagged web, dense in some places and scant in others—loosely mirroring the concentration of people in the country. Here’s Kosara, who runs the data visualization blog eagereyes.com, in a blog post explaining how his viz builds on a postal code dot map created by Ben Fry:

The patterns and density distribution are readily apparent, and can in fact be seen much better than when only the dots are drawn. The scribbling quality of the lines (looks like somebody was bored while talking on the phone) lead to the clever name for the map.

To add some clarity to the monochromatic ZIP code map, Kosara colored the geometrical tumbleweed in each state with a different hue. The resulting map reveals how manmade boundaries (like state lines) and natural topography (like rivers and mountain ranges) affect ZIP code distribution and density:

Kosara’s interactive version of these maps lets you zoom in really close on the tangle of lines connecting these numbers. It also includes Hawaii and Alaska. Here’s a screenshot of a zoomed out version of the U.S. map:

And here are some of the northeastern states up close:

Kosara’s maps aren’t restricted to the U.S.—some feature postal codes from countries around of the world. Below are some of the ones that look like they were created when a polygraph machine went awry. Check out the rest here.

India

Japan

Germany

Iceland

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