It can get pretty quiet here. See Bostonography or Axis Maps for some other posts.

Why are choropleth Mercator maps bad? Because we said so.

The other day I was speaking to a non-map person about the problems with choropleth mapping on the Mercator projection and went looking for a link to something that could explain it more clearly than my bumbling self. It became a familiar exercise, because I’ve done this before: there’s hardly anything out there on the web that really explains this problem in clear detail. We talk about Mercator choropleth maps often enough, and the idea of them ranges from ill-advised to anathema, but we hardly go beyond simply saying “it’s bad because areas are distorted.”

So, two things. First, we could stand to share knowledge better, cartographers! Everyone is pretty good at sharing code and data these days, but we fall short on sharing the why of things, especially those of us who went to school for this and everything.

Second, an attempt at uncovering the problems with choropleth mapping on the Mercator projection.

Now, perhaps nobody really talks about why small-scale Mercator choropleths are bad because the gist of the reason is intuitive enough: bigger looks like “more,” so any map projection that distorts area (especially as severely as Mercator does) will make some values look exaggerated and will thus be misinterpreted. Size comparison is at the heart of many types of statistical graphics, and obviously relative sizes need to be correct for the whole concept to make any sense at all.

Distortion on the Mercator projection

Indeed, this sometimes applies to areal mapping, for example “land-use or similar mapping in which a measure of the area occupied by some distribution is crucial to map interpretation” (Muehrcke and Muehrcke, Map Use 3rd ed.). If you need to compare areas, areas cannot be distorted. (Never mind that humans are terrible at estimating and comparing areas of irregular shapes, from what I hear.)

In the typical choropleth map, however, area is not directly the visual variable of interest, and we are not trying to measure it. Still we assume that relative sizes need to be true in order for the map to work. How do we know that? Well, I’m not sure. I flipped through all my cartography textbooks and to my surprise it’s not that I forgot the evidence for this—it’s that they really don’t cite anything on the subject. We accept it on faith and common sense, apparently, although I’d bet a shiny nickel that someone somewhere has done empirical studies to confirm it, or that somewhere buried in How Maps Work is an explanation. Please, if anybody can point me to some of the research behind all this, it would be appreciated!

Choropleth and proportional symbol maps

It turns out, then, that this is not just an internet problem. A textbook education in cartography will not teach you, in scientific terms, why a choropleth Mercator map is worse than a choropleth sinusoidal map or a proportional symbol map. Interpretation of area in quantitative maps gets no quantitative explanation; instead it gets basically the same treatment as propaganda maps and the whole Peters thing, which paraphrased boils down to “bigger things totally look more prominent and important because they’re bigger.” Semiology of Graphics is the only book I have that really addresses size directly and as matter of fact—noting among other things that “it is not possible to disregard it visually” and “in any map representing areas of unequal size, what is seen is [quantity] multiplied by the size of the area”—but even if he was correct, Bertin was pretty much making things up.

Mentioned more commonly but no more deeply explained is the need to normalize data to account for area in choropleth maps, i.e., not mapping counts. Considering this rule, the projection requirement, and a host of “ideal” enumeration unit characteristics, choropleth mapping just starts to sound like a terrible idea for anything at all. Size variation that is not directly related to numerical variation seems to cause nothing but problems. Danny Dorling’s arguments for cartograms and mapping human phenomena in human space, not geographic space, start to sound appealing.

Too bad cartograms are also kind of awful.

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Free as in painstaking cartography labor

There are ways in which I think cartography is an under-appreciated and poorly understood field, some of which are enumerated in occasional rants on the Axis Maps blog and elsewhere. But these are usually philosophical or academic matters, and as someone who is making a career of cartography, increasingly I’ve been trying to offer this piece of advice (which isn’t as obvious as it should be) to aspiring map people: cartography skills are valuable, as in dollar bills.

Hence my—and some peers’—disappointment in the most recent “challenge” from the MBTA, Greater Boston’s transit agency. To summarize a somewhat lengthy description page, they are essentially seeking new design ideas for their standard subway map—in the space of three weeks, for free, and with no rights retained by the cartographer. And if you win this contest? You get… um, fleeting glory, apparently.

MBTA map

I want to like the idea. The MBTA carries crippling debt, and as a somewhat regular user of the system I don’t want to see its service diminished or my fares increased, so I applaud any other funding or savings. But—and I’m looking for some kind of “third rail” wordplay here—this time they strike a nerve with those of us who have mapping jobs.

The T has run contests before. The most successful was a few years ago at the dawn of its open data age, resulting in some cool visualizations and interesting apps using schedule data, which shortly thereafter was supplanted by real-time tracking. These previous contests, though, were very much about openness. Yes, the clever angle was to get the community to create products at no cost to the agency, but at least these products were not owned by the agency. And there totally were prizes.

From the outside it’s easy to mistake modern cartography for a free endeavor driven by some desire to improve the world. Indeed, we do have a few altruistic motives, and the latest trends are all about openness: open data, open source code, etc. But even these things are not always free. Free to use, yes, but often enough someone has paid for them to be made in the first place. And this model doesn’t really apply to design. Good design is a part of any project, open or not, but when the job itself is design, we don’t jump at the chance to do it for someone else without compensation just because it’s fun. Like everyone else in the world, we do this to earn a living.

In short, if you can design a subway map that’s good enough for millions of people to use on a daily basis, you are very good at this. Maps are easy. Good maps are not. Your skills are valuable. Make maps for fun when it’s for your own satisfaction or for the causes you champion, but recognize your worth when it’s for others’ satisfaction. And make them recognize your worth, too.

In any case, while we’re on the subject, do enjoy Cameron Booth’s MBTA map redesign—which the MBTA can’t have for free—and Peter Dunn’s time-based map.


Silence breaker, 2012 edition

I don’t use this blog much at all these days. As far as blogs go, more of my efforts have gone toward the Axis Maps blog and Bostonography. But in the interest of this site having any purpose at all, I figured I’d jot down some of the things I’ve been up to lately.

  • Hubway trip explorer map: An exploratory tool to see where trips occur in Boston’s bike sharing system. It’s a fairly simple map done in Leaflet that connects to a database of some 550,000 trips and allows the user to filter by a variety of factors of time, demographics, and weather. This was for a contest run by Hubway and MAPC and it won the “Best Data Exploration Tool” award. (Be sure to see the other winners and all the rest!) Finally actually used one of the bikes the other day; pretty convenient!
  • Hubway infographics: For the same contest I also put together a few infographics. There are some pretty bogus charts in there, but I wanted to try my hand and infographicky things, and it was kind of fun.
  • “Why Not The Best” map: We (Axis Maps) completely rebuilt a map we had done with IPRO in Flash a year or two before. Kind of an enjoyable project because I learned a lot of JavaScript mapping techniques; it was only my second real js map project. It’s done with Leaflet and does a bunch of canvas and tile stuff: read all about it.
  • New typographic maps: I didn’t really work on these except for proofreading, but we put out four new typographic map posters this summer: London, Philadelphia, Seattle, and Minneapolis. One that I did work on is a letterpress print of the Boston typographic map.
  • Crowdsourced neighborhood boundaries: A pretty fascinating project looking at the ill-defined boundaries of Boston’s neighborhoods. We made a simple online survey tool in which people can draw neighborhood boundaries as they see them. I mapped some of the data earlier this year, finding where there is consensus (and how much) in each neighborhood.
  • NACIS Practical Cartography Day: At the NACIS conference in Portland in October, I gave a Practical Cartography Day presentation with some tips and thoughts on user interface design for interactive maps, a topic not often addressed there for some reason. The link here goes to the accompanying examples and also has the presentation slides. (Also, I’ll be a co-chair of PCD next year; looking forward to working on that!)
  • “The Aesthetician and the Cartographer”: A rant, sort of, about the superficial view of cartography, and an encouragement to speak more about the why of our maps, not just the how.
  • Newspaper: I had one essay sort of thing for the Boston Globe this summer. Tim Wallace and I occasionally do little features for the Ideas section, but usually one of us has made a map. This time it was about some old-timey satire. That link may require a subscription; I’m not sure. Here’s the blog post that it’s based on.
  • On the nature of web cartography: This link is already a year old, but it’s a recurring topic. Last year I spoke to cartography students at Middlebury College about the processes and philosophies we have at Axis Maps, along with a few practical tidbits. This spring I spoke about similar things to cartography students back in good old Science Hall at the University of Wisconsin-Madison.
  • Send me your high-tech mapping tutorials! I am the section editor for “On the Horizon” in Cartographic Perspectives. We’re still looking for tutorial submissions to this section, so hook us up!
  • Atlas of Design plug: This is not my work, but it deserves many plugs! The Atlas of Design, edited by Daniel Huffman and Tim Wallace, came together quite nicely and was launched at the NACIS conference. It features 27 awesome maps selected from the many submissions they received. Actually, you can’t get it now because it’s sold out, but put yourself on a waitlist to encourage a second printing.
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The end of imagination

Looking dusty here. Tap, tap. Is this blog still on? Here’s an anecdote and a thought.

As much as a decade ago, I remember running into amazingly high resolution aerial imagery of Cambridge, Massachusetts. You could see people in this imagery, which was not so common on the web at the time. I explored Cambridge a bit via the map, as I am wont to do with any map in front of me. I found what looked like some busy spots, identified the famous Harvard University, and so on. It was a strange, unknown place—a city I only knew in person as a collection of buildings glimpsed from highways or from across the river in Boston, where I had been a number of times. It was mostly only a place on a map, and it was up to my imagination to picture what it was like to be there.

Harvard Square aerial circa 2001

Aerial image of Harvard Square, dated 2001 in Google Earth.

Then, some years later, circumstances brought me to Cambridge as a resident. Now a further four years after that, I obviously have a much different image of the city. I love this place, and I’m glad I’ve come to know it well, but there’s no longer any mystique. I kind of miss imaginary Cambridge.

Part of maps’ broad appeal is that they are captivating as canvases for imagination. They can represent lands we’ve never seen, offering a simple lattice of information but requiring us to fill in the gaps in our minds. We can explore maps and “know” places to be as fantastic as our minds will allow. Ultimately, I think, it leads us to explore the places in reality, and it can be shocking when reality doesn’t match our imagined expectations. The shock is not necessarily bad and may even be pleasant (except when, say, imaginary beauty turns out to be a trash-strewn real world); but if you’re like me, you lament the demise of the place your mind invented, even if the reality that supplanted it is better.

As web reference maps move toward less and less abstracted representations of the world, some observers have begun to wonder whether people are losing the interest or need to go to explore real places and experience them in real life, because Street View can show you exactly what a place looks like, or Twitter maps can tell you exactly what people are talking about there, and so forth. I remain optimistic that modern maps will not be a substitute for reality, but rather will draw people in to experience what they know is happening in different places. The maps of old may have tantalized people with their sea monsters and blank spaces, but people didn’t stop climbing mountains when someone else had mapped their slopes with precision, and I didn’t avoid walking around town because I had already seen people-level aerial photos. Knowing what’s out there is as much of a draw as not knowing.

No, the victim in the march toward realistic maps is not real-world experience; the victim is imagination and a bit of the fun of reading maps. I don’t cease to imagine places when looking at a map. It’s just that my imagination is increasingly accurate. It used to be that for every place in the world there were actually two places: one in my mind and one on the ground. Soon, perhaps, there will be only one.

RIP, the last imaginary place on Earth.

Map monster from the Carta Marina

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Submit to the Atlas of Design

This is a quick plug for a new publication being put together by NACIS (the North American Cartographic Information Society, also known as the most awesome bunch of cartographers anywhere): the Atlas of Design, which will feature “cartography at its most beautiful, its cleverest, its sharpest, and its most intriguing.” It’ll be the best coffee table book ever!

A couple of our favorite cartographers are out there now rounding up work from all of our other favorite cartographers. If you’ve got a map to show off, submit it for consideration! If you know people who have maps to show off, encourage them to submit! The deadline is February 24; see all the instructions on the Atlas site.

Do it!

Atlas of Design

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Things I hope you want: this year’s typographic maps

Permit me one avaricious advertisement of a blog post this holiday season. We at Axis Maps have several new typographic city maps that have come out since the summer, and, well, we think they make super gifts. Here are the ones I haven’t mentioned on the blog before.

Chicago letterpress: Two-color prints of the downtown area, with a light blue background on the lake and rivers and either blue or black ink for the text. An addition from the poster prints is the inclusion of the ‘L’ transit lines.
Chicago letterpress map

San Francisco letterpress (2nd edition): In either blue or black ink, this one features a waterline effect around the city.
San Francisco letterpress map

Manhattan letterpress: Two sections, upper and lower Manhattan. Available individually or as a set; with careful cutting you could splice them together and everything will properly line up.
Manhatttan letterpress map

Madison, Wisconsin: The old Axis Maps stomping grounds and home of our graduate institution, the University of Wisconsin. This one is a regular offset print and covers the isthmus and university areas.
Madison typographic map

Besides those we’ve got our old standard posters: Washington DC, New York, San Francisco, Chicago, and Boston.

So there it is. Get in any orders by this Friday to ensure delivery by Christmas!

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