A world made of columns

Sixty-four thousand eight hundred columns, one for every degree of latitude and longitude, standing in for the surface of the earth. Switch what they're showing and the whole field reads itself again. Every view is measured data: nothing here is invented to look good.

The ten views

Elevation is height in real metres, land and sea floor alike, from the same global model that feeds most web maps. Permanent ice comes from its own layer rather than from the height, so Greenland and Antarctica are drawn as ice instead of as brown upland, and the open sea carries a slow swell. Terrain measures how sharply the ground changes rather than how high it sits, so mountain chains, coastlines and the mid-ocean ridges stand out while plains and abyssal basins stay flat.

Ocean currents is the one view here that is drawn rather than measured, and it is drawn because the thing it shows cannot be photographed. What people mean by the Greenland pump is a single loop running through the entire depth of the ocean: warm water travelling north along the surface of the Atlantic, giving up its heat to the sky over Europe, growing cold and salty and heavy enough off Greenland and Iceland to sink two miles, and then creeping back south along the sea floor. No map of the surface can show the half of it that is underneath. So the loop is drawn as a loop.

Follow one crest and you can go round the whole circuit. It leaves the Caribbean warm, runs up the eastern seaboard as the Gulf Stream and across to Europe, cools all the way, and turns dark where it sinks off Greenland. It comes back down the eastern side of the Atlantic cold, joins the Antarctic Circumpolar Current and travels east under Africa, Australia and South America, turns north into the Pacific and warms as it rises, and then returns west through the Indonesian passages, across the Indian Ocean, round South Africa and up into the Atlantic to where it started. A cubic metre of water takes something like a thousand years to make that trip.

Warm water is warm-coloured and always running away from the equator; cold water is dark and running back towards it. The same rule draws the five subtropical gyres, thinner and quieter beneath the conveyor: each ocean turns its own wheel, warm up the western side and cold down the eastern, which is why the Gulf Stream is warm and the Canary Current cold, why the Kuroshio is warm and the California Current cold, and so on in every basin on both sides of the equator.

Two things to be straight about. The loop appears to cross itself in the South Atlantic, where the cold water going south meets the warm water coming north. That is not a mistake in the drawing: in the ocean one of them is two miles beneath the other, and a flat map has nowhere to put that. And the ribbons are a schematic, positioned by hand from the standard published route, not a measurement. The measurement is still there underneath them — the dim blue field is the real, filtered surface velocity, so the ribbons can be checked against the water they are drawn over.

Population turns height into headcount from 1800 to today. Density divides that by how much ground a cell actually covers, since a one-degree cell near the poles is a fraction of the size of one at the equator. Growth shows not the total but how fast it is growing: the population figures are stored as logarithms, so the step from one decade to the next is a ratio rather than a difference, and what is drawn is the rate of increase. That is where the demographic transition becomes visible as it moves across the world.

Empires runs from 500 BC to 2010. Each cell is coloured by whichever state held it, and stands as tall as that state was large at the time, so empires rise and subside as they gain and lose ground. Rome is worth watching: two cells at 323 BC, forty-nine by 200 BC, then the whole Mediterranean.

Continents is the only view where the ground itself moves. Every other view on this page stands on the modern coastline; this one runs from 250 million years ago to the present, and the coastline is whatever it was at the time, so columns rise where there was land and sink where there was ocean. At the far end of the slider the continents are gathered into Pangaea with one ocean wrapped round the rest of the planet, and from about 180 million years ago it comes apart: the Atlantic opens as a narrow sea between what will be Brazil and what will be west Africa and widens ever after, North America pulls away from Europe with Greenland caught between them, and Australia stays pinned to Antarctica until the last fifty million years.

Every landmass keeps its colour for the whole 250 million years, so a piece of ground can be followed from Pangaea to now. The one to watch is India, in magenta. It sits at 47 degrees south for the first hundred million years, is still at 36 south at 100 Ma, and has crossed the equator by 50 Ma — the fastest long journey any continent has made, ending in the collision that is still lifting the Himalaya today. Point at any land and the readout gives the latitude it stood at then and the latitude it stands at now.

Two things to keep in mind. Land near the poles is enormously exaggerated, as it is on every rectangular map: the Cretaceous Arctic really does carry land almost to the pole in this model, but it covers far less ground than the bar across the top of the screen suggests. And the sea floor drawn underneath is the modern one, kept deliberately dark, because the ocean crust of 200 million years ago has long since been pulled back down into the mantle and no map can show it.

Sunlight is the only view that is not a stored grid. The position of the sun is worked out from the clock and the earth's orbit, the same arithmetic behind any sunrise table, and the map is lit accordingly: height is insolation, the share of a sunbeam a patch of ground actually catches, and the colour runs through the real twilight steps down to eighteen degrees below the horizon. It moves in real time. The slider runs the clock forward instead, from a day in a few seconds to a year in a couple of minutes, which is where the tilt of the earth shows itself as the lit band slides north and south.

Cloud cover is the only view that leaves the page to get its data. It asks Open-Meteo what the sky is doing at this moment on a ten degree grid and hangs the answer as a translucent deck above the world, with the ground darkened where the deck is thick, because a cloud that stops light reaching the sea is the same cloud that is bright from above. Tilt the view and the deck stands off the map. The answer is kept for half an hour. Ten degrees is coarse: it is enough for the shape of the weather, the cloud belt along the equator and the clear subtropical highs, and not enough for a particular sky. Pointing at a place asks about that place exactly, and reports cloud, temperature, wind and the sunlight actually reaching the ground.

Moving between moments

Two kinds of change need two different treatments. Quantities, like population or current speed, are interpolated: any year between two records is a genuine blend of the two, so scrubbing the slider glides. Territory is not a quantity. Who holds a piece of ground is a category, and averaging two categories produces a state that never existed, so instead each cell hands over on its own offset within the interval. A hard switch becomes a border that sweeps across the ground.

Playback does not run at a constant rate. A timeline held to one speed treats two uneventful centuries exactly like the year the Western Empire fell, so instead it runs fast between the moments worth stopping for, eases down as one approaches, holds for a couple of seconds while its name is on screen, and picks the pace back up. The slowdown reaches much wider than the caption does, so the change of pace is gradual while the name itself stays punctuation rather than furniture. Parking the slider next to a landmark names it too, without playing anything.

The landmarks are chosen, not derived, and the dates are the conventional ones: the billions on the population clock, the rise and fall of states on the territory run, and on the drift the breakup of Pangaea, the opening of the South Atlantic, the impact that closed the Cretaceous, and the collision of India with Asia.

Getting around

The map behaves like a map rather than like a model on a turntable. Drag takes hold of the ground and moves it. Scroll zooms towards whatever is under the pointer, so you can put Australia in the middle of the screen and keep going until single columns fill it. Shift-drag, or the right or middle button, tilts and turns the view: flat overhead for reading the shapes, low and oblique for reading the heights. Arrow keys pan, plus and minus zoom, and reset view puts everything back.

The opening framing shows the whole world rather than filling the window, so the far east and west of the Pacific are both there from the start.

Hovering

Point anywhere and the map reports what it knows about that cell: elevation in metres, current speed and heading, the country and its population for the selected year, or the state that held the ground and how far it reached.

Sources
Elevation, land and sea floor: Terrain Tiles on AWS, the open global model assembled from SRTM, GMTED2010 and ETOPO1. Sampled to this one-degree grid; values are metres.