Earth Xray

Here’s a little project I’ve been thinking about for a while, and finally managed to cobble together over the summer – Earth Xray is a mobile VR website that renders a 3d “x-ray” of world geography as it exists in real-world, physical space below your feet. It’s sort of like one of those astronomy apps that traces out an atlas of constellations when you hold the phone up to the sky. But, flipped upside-down – instead of stars in the sky, Earth Xray draws a regular atlas of political geography as it exists “underground”, hidden by the surface of the earth as it curves away below the horizon:


So, for example, if I put the phone flat on a table, the app renders a line straight down through the center of the earth to the far side of the world, 7,917 miles away – here in San Francisco, somewhere in the chilly waters between Madagascar and Antarctica. To the east, the outlines of the United States arc up towards the camera, California wrapping around the edges of the screen. Europe and Africa are down and to the left, tucked behind the filing cabinet next to my desk. Mexico and Central America curve down to the south, behind the keyboard. To get Australia and Southeast Asia into view, I have to swivel the chair around and look almost straight down:

Bring your own dramamine.

To give a sense of depth, the scene draws a little 3d sphere at the intersection point with the far side of the world, which grows and shrinks as it gets tugged around to different coordinates by the orientation of the phone. And, at the top right of the screen, the app prints out the compass bearing from your location to the center point, along the “great circle” route connecting the two points (the shortest path across the spheroid of the earth). In a 3d context, this surfaces some funny and unintuitive geographic facts. For example – from San Francisco, the fastest way to get to Iran is to go almost exactly due north, straight up through British Columbia, over the north pole, and down through western Russia.

Now, it goes without saying, this is only as accurate as the compass on your phone. Which is a mixed bag – sensors on modern devices are pretty good most of the time, but not always. For instance, they’re very susceptible to local magnetic interference – if you hold a phone next to a computer monitor, or even another phone, the compass is often no better than random. And, some devices are just hopelessly miscalibrated, and give totally incorrect readings. So, you know – don’t use this to launch missiles, or whatever.


I’ve spent a huge amount of time over the course of the last few years staring at 2d maps on computer screens. After a while, this starts to seep into your mental model of the world – Japan is “left,” San Francisco is “up,” the east coast is “right,” Mexico is “down,” etc. I’ve been thinking about this when I walk into work in the morning, heading west along Palm Drive from the train station. It’s a lovely view – I look out over Stanford at the mountains on the peninsula, a dark green line covered with white clouds, like a huge tidal wave coming in off the ocean. I’ve realized, though, that there’s an incessant little mechanism in my head that’s constantly trying to snap the actual sight of the mountains onto the blue-and-beige memory of the corresponding OpenStreetMap tiles. I’m looking at the mountains, but I’m often actually seeing the map, burned into the back of my skull by thousands of hours of pushing pixels around on Leaflet and OpenLayers.

Long-distance backpacking is the perfect antidote to this. Back in June, I did a 7-day loop on the Tahoe Rim Trail, a gorgeous 165-mile walk along the ridgeline of the Sierra Nevada that circles around the lake. Hiking reminds you that the world is a physical thing, not just some kind of mathematical abstraction. The lake shifts and morphs as you move around it – mountains rise up in front of you, sink below your feet as you climb on top of them, and then recede into little bumps in the ridgeline as you drift away along the trail. And, Tahoe in particular is a kind of grand meditation on the Z-axis, on depth, on the three-dimensionality of the world. The lake is lofted 6,200 feet above sea level by the mountains – if Denver were kept at the same elevation but shifted 800 miles west, the city would be completely submerged inside the lake. The tip of the tallest building in the city, the 714-foot Republic Plaza, wouldn’t even nip up above the surface of the water. At the end of the trip, wading in the water at Speedboat Beach with Kara, we were more than a vertical mile above the apartment in Menlo Park. If the mountains disappeared, it would take 40 seconds [1] to fall back down to sea level.


Three days out, looking north from Freel Peak (10,886′), the highest mountain on the rim. Tahoe is is on the left at 6,224′, 39 trillion gallons of water held up by the mountains. Carson City, eight miles away in the patchwork on the right, is about 1,500 feet lower at 4,697′.

And, beyond questions of elevation, there’s the even more trite-but-dizzying thought that the curvature of the earth introduces enormous “vertical” offsets when you start to think about distances at the scale of countries or continents. The town in Alabama where I grew up, for instance, is about 1,965 miles away from where I am right now in northern California. In that distance, though, the surface of the earth curves down about 14.2 degrees, putting Tuscaloosa 478 miles “below” Menlo Park. Of course, this muddles the notions of “up” and “down,” which shift along with the curvature of the earth – in Tuscaloosa, it’s Palo Alto that’s “down,” not the other way around. But, given that we always inhabit one particular point in space, there’s the very real sense in which we’re standing at the top of the world – each at our own little personal north poles, the earth a huge ball falling away around our feet. Los Angeles – a 6-hour drive south – is 15 miles below San Francisco. In the 2,189 miles between Georgia and Maine, the Appalachian Trail sinks 590 miles. Scenes of old adventures in Spain and France – San Sebastian, Hendaye, the Camino Santiago, Finisterre, the Pyrenees, the week I spent squatting in vineyards on the Riviera – are deep below my feet, 3,590 miles down, a 60-hour drive straight into the ground.

Anyway, somewhere on the way around Tahoe I realized that I had lost an intuitive sense of the world as a 3d object. (Or, maybe I had just never had it in the first place.) How to fix this? Could I write a piece of software that would chip away at the spherical mercator worldview – somehow sidestep the questions of projection and representation and just show the world as it actually exists in the physical, 3d “meatspace” in front of my eyes? How to unproject the world, re-three-dimensionalize it, restore a sense of depth?

Happy x-ray-ing!