30 August 2007

ways of drawing the Interstate Highway System

Earlier this year, Chris Yates made available online a simplified map of the Interstate highway system, where the interstates are for the most part straight lines. This made its way around the Internet for a while, and it was frequently pointed out that it was wrong -- certain interstates just aren't on it. (The ones I noticed were I-83 (which runs between Harrisburg and Baltimore) and I-88 (Albany to Binghamton); a lot of other people pointed out that it also omits the entire state of Wisconsin.)

It occurred to me that it would be nice to see this map done correctly, and I'm trying to do it myself; unfortunately I don't have a really big piece of paper! It's probably possible to represent all the two-digit Interstates on a single piece of paper, though. But this map from Hedberg Maps looks like what I was thinking of -- it basically assumes that as many of the two-digit Interstates as possible actually form a grid and then fills in the rest, including the three-digit Interstates, accordingly. Too bad it's $40. They explain how the map works here; basically, the map's author, Nat Case, attempted to respect the topology of the system and align the main roads of the system with the grid, so the distance between, say, I-70 and I-80 is the same as the distance between I-80 and I-90. (Case claims inspiration from Yates' map, but seems to be a lot less visible on the Internet, probably because you can't view it online.)

A lot of people compare these to "subway maps", but there's one big difference. On a map of a subway system, the various subway lines are generally denoted by different colors; this makes it obvious when one has to transfer from one line to another. (See, for example, the standard Washington Metro map; there's a recolored version of the map to indicate the different service patterns they run on July 4th.) And this makes sense, because a change of trains has a substantial cost -- you've got to get off the train, often walk up or down some steps, and wait for another train to come. Roads don't work like that -- the cost to go from one highway to another is minimal.

I'd also like to see a similar map of, say, Philadelphia; the street signs indicate that each intersection is a certain distance west or east of one axis (Front Street or Germantown Avenue, depending on location) and north or south of another (Market Street), but the grid breaks down the further you get from the historic city. I actually live along a "seam" in this grid; as you walk down my street the numbers immediately go from the 500s to the 900s. How is the map distorted if you try to place locations not where they are, but where the addressing system implies they are?

edited: Nat Case talks about the map at mapHead; you can see a larger version of the map here. (1080 by 1080, which is large enough to get a very good idea what's going on. It's particularly interesting how some of the shapes of states get distorted here -- Florida is now much longer east-west than north-south, for example, and Arizona and New Mexico end up having roughly the shape of Chile, and Illinois is huge.

Personally, I think it's a little crowded in the northeast, which is something you might not necessarily expect from the description.

And now I don't have to make this map myself to see what it looks like, which is a relief because I'm not particularly good at this sort of thing.


John Armstrong said...

I wonder if the Hedberg map shows the whole system, including such esoterica as I-595 in Maryland.

btw: I like the new look.

Isabel said...


to get an idea of the level of detail, there are two "detail" maps available, for the Kansas City and Washington areas. It turns out that I-595 is visible in the Washington detail, and furthermore is displayed differently to highlight the fact that it's not signed.

Bill Mill said...

I sent the company a request for a nicer thumbnail, and who I presume to be the map author responded in minutes with a very nice 1080x1080 thumbnail.

natcase said...
This comment has been removed by the author.
natcase said...

Hi, thanks for the link Bill, and thanks for the mention of the, um, well I guess it's a map more or less.

I talk about the thing on my blog, MapHead. There's a link to the thumbnail Bill mentioned. Here's a direct link. Sorry it's not up on the Hedberg Maps catalog site. We're working on that weakness in the site...