Humanistic Approaches to Data Visualization

In March 2013, Cameron Blevins came to me with a question about how to visualize his research into the U.S. post office. This presented a fantastic opportunity for both of us: as a research collaboration and a chance to learn d3.js.

What do you do with 14000 post offices?

DH likes to ask what to do with a million books. I wanted to ask what to do with 14,000 post offices. We wanted to know – what insight could we gain from visualizing the Post?

White on visualization

Visualization, as historian Richard White argues, is a means of doing research: of posing questions we otherwise could not ask without the aid of computers; of identifying patterns that might otherwise go undiscovered.

The design of the project went through several iterations as we tried to solve a key question: how to present the data in a meaningful way. Plotting points on a map is a simple enough exercise, and I find even that process can be arresting—to see the massive network of the Post and where communities tended to cluster in the West. But we wanted more than just the presentation of points on a map—we wanted to represent knowledge.

Offices in Oregon

Our iterations of the project were straightforward. Our test case focused on Oregon, and we started plotting offices onto a Google Map using the JavaScript library D3.js to begin understanding, first, how the technology would work, and second, what sort of things could we begin to do with the data. We experimented with alternative views as well. Rather than viewing points on a map, could we put post offices into a bin and get a sense of geographic concentrations? We tried with hex binning—a hexagonal grid for creating histograms that allows us to interpolate values between point on the map. An interesting view, perhaps, but does it help us answer or raise new questions? Such a map help us visually understand geographical concentrations of post offices, but our data let us ask an even more interesting question: where are people going in the American West? We needed interactivity.

We had a lot of data – complex, messy, incomplete data. The entire dataset is 160,000 post offices for two centuries for the entire US – we only focused on the latter half of the western US.

In some ways, the data we worked with didn’t present a lot of challenges: it’s complex, yes, but the data is all the same. We were not confronting, say, a digital archive of texts, all of which can be radically dissimilar in their form and content: case files, advertisements, newspapers, diaries. We didn’t have to confront what William G. Thomas has called the document-type problem. But there were other design challenges: for example, meshing together datasets. Cameron began the project with an already-massive dataset of post offices, but roughly eight months ago he purchased another dataset from a stamp collector that expanded the amount of evidence we worked with massively. He now have data for the entire United States. Thus, we are confronted with the architecture of our data. Then we had to ask the really dangerous question: Where does the West begin?

Where is the West?

Part of our argument is that we can use the post office as a proxy for understanding settlement patterns in the West. Many of these nineteenth century towns died years ago; they don’t exist on present-day maps. The West is known for its ghost towns – we can see a lot of them here.

I want to make a case to you today about why we should think about the Post as a proxy for communities, and the significance of visualizing that process.

There are, of course, many ways we could represent population figures visually. One of the more popular techniques is choropleths. But there’s a problem with the chropleth when it comes to the West: we have what Cameron has called the West’s “county problem.”

County problem

The problem with western counties is that they’re huge. Look at San Bernardino in Southern California, which includes the metropolis of Los Angeles. Lots of people, right? but the actual population is huddled against the western edge of the county rather than evenly distributed through the county. You get a visual representation, then, that can be misleading. What you want is more granularity.

Let’s focus on Colorado and New Mexico in 1870 – keep these places in mind, we’ll return to them a few more times. We get a sense that there are lots of people, a rough idea of where they’re at in the states with the choropleth. But it’s hard to really know unless you compare this with our map.


Two things stand out to me here. One, these two things map onto each other well. If we overlaid the population data with the post data, I think we’d see that the shading of the counties would fit well with the location of post offices. But, we also get a better sense of where people are at. They’re not distributed throughout these huge counties in New Mexico; they follow a corridor north to south – probably a railroad line in New Mexico, and nestled against the Front Range in Colorado.

To me, this is significant. If my historical question is about the settlement patterns of the western US, it matters a great deal to me to know where exactly those communities are at. The Post gives me a window into that process.

Post as Proxy

So, the Post becomes a proxy for a town. You wouldn’t have a post office where there’s no town. This is the way people communicated in the nineteenth century; oftentimes, these towns were not located next to railroads. They needed the Post and its network of postal roads, stagecoaches, and rail lines to distribute news and information. This was your connection to the broader world. It was also a key part of the national government’s process of folding the West into the national. Rather than an isolated region, it became integrated into a national system of information. And this network connected the West to larger social, economic, and political networks.

But maybe you don’t believe me quite yet. Maybe you look at these offices and say: this doesn’t work. There’s no story here. Let me give you one more example; I have to give a shoutout to Ben Schmidt, a historian at Northeastern, for alerting me to these maps.

1915 Statistical Atlas

In 1915, the U.S. Census Bureau published the Statistical Atlas of the United States. It’s a beautiful book filled with some stellar visualizations. One set of visualizations sought to illustrate the population density of the United States for 1870, 1880, and 1890.

I looked at these maps and thought: does the postal data map onto these. In other words, can I really treat the post as a proxy for settlement? If post offices happen to line up well with the Census bureau’s own statistics, to me that’s further evidence that I can treat these as indications of settlement. So, let’s look.

Colorado-New Mexico

Here’s our Colorado – New Mexico corridor in 1870. I apologize that my projection is different from that used by the Census Bureau, so you may have to squint a bit to help. Looking at these side-by-side, I think they pretty accurately map onto each other. Notice the small pocket of post offices to the west of Denver; that same blob appears on the Census map to the west of Denver. Notice the collection of offices in northern New Mexico; the Census map distribution shows that same presence.

So, we have the West of 1890 – heavy populations in California and the Pacific Northwest; lots of people along the Rocky Mountains; empty areas in Nevada and Utah and Montana. My map seems to map onto this pretty well. Pay particular attention to WA, OR, CA – my projection isn’t the same as the Census, so they don’t map quite right. But they’re pretty close. And if I fixed the projection, I think they’d map onto each other very closely.

So, comparing post offices to other maps and visualizations – I’d say that we can safely use the Post as a proxy for understanding communities. But the question is, why is that important? Why did I spend all this time trying to convince you that I can safely treat the Post as a proxy for communities?

Because the story isn’t just about the rise of communities; it’s also about their decline. You don’t see this in the Census maps.


If we look at the progression of the maps from 1870 to 1890, the maps tell a particular story: one of growth, one of progress. Let’s return to our Colorado - New Mexico corridor. What you don’t see in these is the communities that don’t thrive.


Here’s our corridor in the Southwest again; these are post offices that close between 1870 and 1890.

If the story I’m interested in is the process by which communities grow and decline in the West, it’s these communities I want to examine. Again, you don’t see these places in the Census Maps. I would bet you also wouldn’t see these changes using population data for counties. But the postal data we have can give us that.

And therein lies one of the great benefits that I think visualization lends to the humanities. The Census maps are static, giving me snapshots of particular moments in time. Our map lets you examine any moment in time between 1848 and 1900. Maybe your curious about what’s happening in western settlement during the American Civil War? You can select those years. Maybe you have a particular interest in western settlement as conflicts with Native Americans are happening throughout the west in the 1870s and 1880s. You can select those years. You can look at places where communities go away and where they spring up – and that’s key.

What the map does is lead me to questions. It leads me to places on a map that may be overlooked by historians. Some of these places no longer exist; they, quite literally, are removed from the historical record. Some of these places are mining camps – they exist only for a year until the mines run dry, then they’re off the map. What’s happening is a distant and close reading of a spatial experience. By stepping back and looking at overall patterns, we can then zoom in closer – track down more sources, track down more information, give richness to the fabric of historical experience.

January 18, 2015 @jaheppler