Visualizing Ocean Shipping

I saw some historians talking on Twitter about a very nice data visualization of shipping routes in the 18th and 19th centuries on Spatial Analysis. (Which is a great blog--looking through their archives, I think I've seen every previous post linked from somewhere else before).

They make a basically static visualization. I wanted to see the ships in motion. Plus, Dael Norwood made some guesses about the increasing prominence of Pacific trade in the period that I would like to see confirmed. That got me interested with the ship data that they use, which consists of detailed logbooks that have been digitized for climatological purposes. On the more technical side, I have been fiddling a bit lately with ffmpeg and ggplot (two completely unrelated systems, despite what the names imply) to make animated visualizations, and wanted to put one up. And it's an interesting case; historical data was digitized for climatological purposes, which means visualization is going to be on of the easiest ways to think about whether it might be usable for historical demonstration or analysis, as well.

So here are two visualizations.

[Update 11/12: For more of this, see my discussion of American shipping, and whaling in particular, from 1800 to 1860.]

The first one is long: it shows about 100 years of ship paths in the seas, as recorded in hundreds of ship's log books, by hand, one or several times a day. I haven't watched the whole thing at once, but skipping around gives a pretty good idea of the state of the database (if not world shipping) at any given moment.


You can watch either of these in much higher resolution by clicking around here or on YouTube--I definitely recommend 720p.

This shows mostly Spanish, Dutch, and English routes--they are surprisingly constant over the period (although some empires drop in and out of the record), but the individual voyages are fun. And there are some macro patterns--the move of British trade towards India, the effect of the American Revolution and the Napoleonic Wars, and so on.

The second has to do with seasonality: it compresses all those years onto a single span of January-December, to reveal seasonal patterns. I loop through a couple times so you can get a better sense, but the data is the same for each year.





There aren't many truly seasonal events, but a few stand out. There are regular summer voyages from Scotland to Hudson's Bay, and from Holland up towards Spitsbergen, for example: both these appear as huge convoys moving in sync. (What were those about?) Trips around Cape Horn, on the other hand, are extremely rare in July and August. More interestingly, the winds in the Arabian sea seem to shift directions in November or so. I also really like the way this one brings across the conveyor belt nature of trade with the East.

19th century ocean trade isn't exactly much my field, so I don't have much analytically to say about these. I'm hoping Dael might. I tend to generally think this source won't be that useful to historians, because it's such a funny set of ship's logs--dictated by climatological needs, by EU priorities, and so on. But there may be certain questions.

• You get some individual voyages of interest. The Battle of Saldanha Bay (1796), when a contingent of Dutch ships sail south and engage with the British in August by the Cape, is clearly visible on the map; so is much of the Resolution's route on Captain Cook's second voyage (1772-1775) through the South Pacific, including its southernmost point. Some other events--the massive Spanish convoys in 1778 leaving from Peru, for example--I can't place as easily. The Beagle, unfortunately, is not represented.

• This is nothing resembling either a comprehensive list of ships, or a random sample of the same. The world's seas, for example, were not actually entirely Dutch controlled in the mid-nineteenth century.

• The Pacific is, as I said, almost completely ignored in the records. Still, I'm amazed at how consistently the voyages end around Singapore/Batavia rather than proceed up to China and Japan. Dael's the expert on Pacific shipping, maybe he has something to say on this.

• Relatedly, so are the United States--possibly since this is biased towards naval vessels, and the US was mostly trading, possibly since this is an EU project. But French ships are almost as poorly represented.


A few more notes, though I think most things here are pretty self-explanatory. Each ship leaves a dimming trail behind it. I set them for four days long for the one-year visualization, and 180 days for the 100-year one. That lets one see more clearly, for example, that what appear to be two different trade routes on some maps are simply out-and-back on prevailing winds. On a long scale, this lets you see individual voyages; on a short one, predominant direction.

The basic code that got me started with the data was posted by Einar in the comments on Spatial Analysis. Logbooks aren't consistent, and so have to be massaged--I use ship and logbook names to separate voyages in the data, and don't connect any points separated by 60 days or 30 points of longitude/latitude. The basic idea for that is the same James Cheshire used for his maps on Spatial Analysis. The shapefiles for the continents are from Natural Earth Data.

You see a blink in the year charts at January 1st--that's a bug. You see another one at March 1: that's because 3/4 of all the ships disappear from the seas on February 29th every year. I just left that one in, because it's interesting.

Seasonality is a geographical phenomenon as well as a temporal one, so I positioned the month labels directly beneath the location of the sun at noon over Africa. This looks better to me than a time ticker, and captures the way the location of the sun enables greater sailing. I actually wanted to rhythmically deform the projection according to the position of the earth in space, but turned out to be a bad idea on a couple of counts. One of them is just how much the globe rocks back and forth--it's really kind of scary.

I use Gilbert's two-world perspective for the plot, because it gives a nice view on the Atlantic and Indian oceans, while wreaking havoc on the Pacific--that maps nicely onto the data sets. I thought about something more elaborate--like the "Lotus" projection used to display the oceans in the 1954 Times Atlas--but my GIS skills are not quite there. (And neither, unfortunately, is the mapproj/ggplot2 combo in R--lots of split lines, confusions on the global level, and so forth. I've been hoping I might be able to give up on ArcGIS for the next map project I do and keep everything in R--I'm not convinced after this experience that it will be possible). In any case: my apologies to any New Zealanders or Hawaiians out there. You are gone, but not forgotten.