Submitted by Dennis McClendon, who has previously submitted material related to transit mapping in Chicago that I’ve featured on the site.

This map is a real beauty, and I definitely appreciate Dennis’ ability to talk about the technical aspects of cartography in the days before computers. We take computer-aided design almost completely for granted today – but map-making was a laborious, manually performed task back then, where a scalpel, a light box and rubylith film were vital parts of a cartographer’s arsenal.

I’m just old enough as a designer to have come in at the very end of this manual era of printing. My very first task in a real design studio was to cut up 48 pasteboards to mount the artwork for 24 double-sided leaflets on. I then marked up each and every board on an overlay with the colour specs for every element and instructions for stripping in photos from colour transparencies, or “trannies” (yes, really):

Tranny X – enlarge to 143%, crop as shown. Strip to keyline, delete keyline.

For every photo on every page.

But enough reminiscing about the olden days: on to Dennis’ thoughts on this fantastic map:

Because I’m hard at work on its modern successor, I thought you might be interested in a very curious and striking printed map from the 1970s: the famous black Chicago RTA map, first published in 1977.

This was the Chicago area’s first full-color transit map, a splashy beginning for the newly created Regional Transportation Authority that voters had approved to take over the region’s failing transit agencies and private companies. The colors used for the Chicago Transit Authority rail lines would—mostly by happenstance—be chosen 20 years later as the actual names for those lines (brown got swapped with purple for the line serving Northwestern University, whose school colors are purple and white).  Transit history geeks will understand the A and B symbols on the rapid transit stations as relating to Chicago’s skip-stop service (ended in 1995) during which alternating trains stopped only at A or B stations.

The system map exhibits several traits long associated with Chicago transit maps, such as the curving corners, dots at terminals, and bare route numbers next to the lines.  There are reminders of the era, like the Souvenir Bold Italic typeface used for points of interest.  The map was designed by Rand McNally, and the folklore is that they were hungry for the work. The same oil crisis that had boosted interest in public transit had made free gas station maps unnecessary, and that was a big part of Rand’s business. But the main design question is: why black? Printing a rich black generally requires two passes, or at least an underlayer of cyan.

The official explanation for the black is that it was a clever way to deal with misregistration of thin colored lines.  Undoubtedly there’s a lot of truth in that.  In those days of Scribecoat and photomechanical production, cartographers had to worry a lot about trapping and misregistration. So a close look at the thin blue and tan bus lines will reveal that a one point line has been photographically “spread” into a 1.4 point line that is behind a 1 point gap in the black (black is printed last in four-color printing). The method wasn’t always totally successful, and there are tiny white gaps around some of the point-of-interest names.  But an ordinary 1 point tan line would have been difficult to print, since it would be composed of a 20 percent dot each of cyan and magenta, and a 30 percent dot of yellow—all of which would need to line up exactly.  None of the colors would so dominate that the other colors could be “choked” to a narrower line that wouldn’t peek out.

Some of the printing details can be seen in the enlargement.  The rich black seems to be 100% black over 40% cyan.  The ocher-olive (not the most pleasing color, even in the earth-tone 1970s) looks to be about 60% black over 60% yellow.  A similar combination of cyan and black produces a handsome steely blue for the downtown inset.

A very curious design feature is that bus lines are never allowed to intersect.  Instead one line is always broken where another crosses it. Some of this was worked out by folks who knew the system well, and buses on overpasses, or buses making a 90-degree turn, are always shown on top of crossing lines. The others were randomized like a basket weave. The reason for this design choice isn’t obvious to me; it may be that it reinforces where lines turn a corner and where they continue straight. There doesn’t seem to have been a production rationale: at least one perfect uninterrupted crossing (Kimball and Peterson) is shown, apparently by mistake. The idea of color-coding bus lines by which rapid transit line they feed wasn’t a success.  Lots of crosstown lines reach four different lines along their lengths, and many crosstown bus riders aren’t headed to a rapid transit line at all.

But back to the main question, why black?  I never saw another example anywhere of a black transit map—except for Métro inset maps on Montreal’s maps in the 1980s, which were so obviously reproduced directly from the artwork used for panels inside the cars that they even include the warning not to interfere with the functioning of the doors.

I think the real reason was marketing. The RTA was a new agency that saw the value of graphic design to tie together the region’s disparate transit assets and build public support for them.  The maps, the signage typefaces, even the livery on locomotive, railcars, and buses was what we would today call “branding.” So while there may have been a good production justification for the striking black RTA map, I think the bigger reason was how cool it looked. Indeed, I had a copy hanging on my wall when I was in grad school a thousand miles away, never dreaming that 30 years later I’d be the designer trusted to make a new RTA system map useful and attractive.