Since day one of the Out of Eden Walk, I’ve been archiving, processing, and visualizing the route’s GPS data captured by Paul and his walking partners. The data points collected every few seconds contain latitude, longitude, date, and time to the second for each step taken. To record the locations of each Milestone, Paul uses a proximity alarm on his GPS that is set to ring when it logs a hundred miles from the previous Milestone, regardless of the distance he's walked to get to that point. This results in equally spaced, straight-line waypoints.
So Paul travels a hundred miles between Milestones, right? Yes, but…
Paul’s actual walking path is anything but a straight, as-the-crow-flies path. He is traveling on foot as a terrestrial being, where undulations of the Earth’s surface must be accounted for and where direct travel is hard to achieve unless in the rectilinear layout of a city or across a flat surface such as desert hardpan or ice. For example, the actual miles walked between Milestones 68 and 69 in India totaled 130 rather than a hundred miles. The trails and terrain across the Brahmaputra River plain and adjacent hills compelled Paul to cover an extra 30 miles between the Milestones.
Paul's actual walked miles between Milestones 68 and 69 are visualized by the green line. From Milestone 69 to 70, his path became squigglier, for a distance of 175 miles (yellow line). Between Milestones 70 and 71, he hoofed a mighty 215 miles (red line), zigging and zagging to negotiate the dense folds of the Arakan mountains approaching Myanmar.
Map courtesy of Jeff Blossom
Sinuosity is the scientific term for how curvy a route is. It’s calculated by dividing the actual distance traveled between two locations by the straight-line distance. The sinuosity calculation between Milestones 68 and 69 is 1.3: 130 divided by 100. Between milestones 70 and 71, the sinuosity jumps up to 2.15 (215 divided by 100). One Milestone pair, between 93 and 94, in Jilin Province in eastern China, has the highest sinuosity anywhere along Paul’s trail from Ethiopia through South Korea—a whopping 3.84. To help understand this outlier, I created a visual depiction of the area in question (also known as a map!). I used mapping software to create a hundred-mile circle around milestone 93, known in cartographic parlance as a “buffer,” to illustrate the extra distance Paul walked.
The white line symbolizes the hundred-mile circle, or buffer, around Milestone 93. Paul started from 93 in a northeastward direction, then, having logged nearly one-hundred straight-line miles, he turned due south, then southwest, accumulating the 384 miles of walking before finally reaching Milestone 94.
Map courtesy of Jeff Blossom
This variability reflects how rumpled and contorted the surface of our Earth is. In Paul’s storytelling, all the equally spaced Milestones are represented with a panorama photo, a photo of the Earth at his feet and the sky above his head, a video of the surrounding landscape, and three questions he asks the nearest person. This storytelling device provides a standardized snapshot all along Paul’s trail, but his walking reality is endless variability of foot-distances traveled, people encountered, and landscapes traversed from one Milestone to the next. For those of you who want to dive deeper, updated metrics for the Milestones can be found in this spreadsheet.
I hope you’ve enjoyed these reflections on mapping and measuring the walk from the perspective of a geographic information analyst/cartographer. I encourage you to ponder the Milestones in your life and enjoy the variable journeys between them.
Author’s Note
Managing the Out of Eden Walk’s GPS data, calculating the distance walked between Milestones, and creating maps is an ambitious task, and over the years, a team of students and visiting researchers have helped. A big thank you to: Lingbo Liu, Devika Jain, Will Jones, Sid Meka, Zach Sherman, Robert Spang, Jacqui Schlesinger, Navya Tripathi, Eamon Breen, and Daniel Weinstein.