Warning: This post makes absolutely no sense to anyone outside the United States, or to anyone who relies on a mode of transportation that uses a sane numbering scheme.

Development on the OSM U.S. shield renderer seems to have stalled a bit, and my request to render pictoral route shields on the Standard stylesheet is effectively tabled for now. There doesn’t seem to be a whole lot to get excited about on the shield rendering front.

Just to bide my time, I decided to approach route shields from the other direction, using OpenStreetMap’s coverage of the Cincinnati Tri-State area as a starting point. Slapping shields in random locations all over a road map is so… functional. So let’s ditch the map, fire up TileMill, and let the shields do the talking:

A bit of a mess, isn’t it? It’s even worse when you zoom out:

But pan around, and you might start to notice some patterns if you’re from the area. You can make out the most prominent highways. Here’s a map Nate made from OSM data, for comparison:

You can make out the Ohio–Kentucky state line where the state route shields in the shape of Ohio turn into plain old circles:

So what’s going on? Each shield on the grid indicates the nearest Interstate, U.S. route, or state route, with an understandable bias towards highways over surface streets. A shield isn’t necessarily positioned along the route it indicates; rather, it just happens that no other route is closer. That property gives rise to an interesting phenomenon that I’ll take the liberty of calling a routeshed. Much like a watershed, a routeshed encompasses the area in which cars naturally flow toward a single route. OK, that sounds so ridiculous it belongs in a Wikipedia article. But this is what the sparse terrain of western Hamilton County looks like:

If you’re as sleep-deprived as I am, it does kinda-sorta look like a watershed.

Here’s the full slippy map.

Credits: Road data from OpenStreetMap contributors, mostly me, Nate, and NE2. Shield blanks from Wikimedia Commons users SPUI, Ltljltlj, Fredddie, and Scott5114. Shield labels set in Roadgeek 2005 Series C and D. Code under the MIT license; tiles under Creative Commons Attribution 4.0.