The Physical Earth

How to read it

Land is coloured by height and lit from the north west, so green is low ground, brown is high ground and white is the top of the range. The sea is drawn in twelve nested depth bands rather than as one flat blue, which is why the continental shelves, the mid-ocean ridges and the trenches all show. There are no borders and no place names: the coastline does the work of telling you where you are.

What this kind of map does well

It needs no key. Almost everyone reads green to brown to white as low to high on sight, without being told.

The structure shows up as one system. Mountain belts, shelves, ridges and trenches connect across the whole sheet. You can very nearly see the plate boundaries without any being drawn.

Shading adds what colour cannot. The bands tell you how high; the relief tells you what shape. A plateau and a dissected range can sit in the same colour band and look nothing alike.

It does not expire. Nothing on it changes when a country does.

Where it misleads

Colour is not climate. This is the big one. Green means low, not fertile, and brown means high, not dry. Western Siberia is green and it is bog and taiga. The Tibetan Plateau reads pale and it is high desert, not ice. The Sahara looks arid here by coincidence: it is simply elevated.

Pale is not always ice. The ice sheets are drawn as their own layer, but high ground with no ice on it can still come out nearly as light.

The bands invent cliffs. A step between two depth bands is a line in the legend, not a feature on the sea floor.

The vertical range is brutally compressed. Everything from sea level to 8,848 m shares a handful of steps, so most of the relief people actually live in, the first few hundred metres, is invisible.

Ice surface is not ground. Antarctica and Greenland show the top of the ice, which is kilometres above the rock.

Green and brown together are a poor choice for readers with red-green colour vision deficiency. The ramp is a layer setting, so it can be changed.

What it is made of

Seventeen layers, and every one of them is in the catalogue. Opening the map in the editor shows them in the order below, drawn bottom to top.

Shaded relief, 1 km.One image, composed offline from the elevation model rather than fetched as survey data. It is the only ingredient here that is ours rather than a publisher's, and the only one that was transformed. The source is Copernicus GLO-90, averaged down to a grid of 36000 by 18000 cells, about 1.1 km at the equator. The terrain is then lit twice over. One pass is fine, and picks out ridges and valleys. The other works from a much coarser copy, and keeps whole mountain ranges reading as single masses rather than as a field of crinkles. The two are mixed together with the fine pass dominant. Colour comes from height alone, and that light darkens it, never all the way to black, so a slope facing away reads as shadow rather than as a hole. Last, the sea is cut out using Natural Earth's land polygons, which is what lets the depth bands show through underneath. Nothing was retouched by hand.

Twelve bathymetry bands, 0 m down to 10,000 m, and the glaciated areas, Antarctic ice shelves, salt flats and coastline: all Natural Earth, served exactly as published and changed in no way. What was chosen here is their colour and their order, both of which are ordinary layer settings you can change. Natural Earth calls the salt flats playas, which is the term in the source data. At world scale they cover only a few hundred pixels, so they read as small pale patches and not much more.

The ice is deliberately a layer and not part of the baked image. Natural Earth publishes it as a land cover, so it is drawn as one: it can be moved, recoloured or switched off. A relief image with the ice already painted into it would be a picture nobody else could reproduce.

How the pieces fit

The relief image goes at the bottom, under everything else, so the ice, the salt flats and the coastline draw on top of it rather than under it.

The depth bands run shallow to deep. They are nested, so the deepest has to be drawn last or it ends up buried under the shallower ones that contain it.

The coastline and the 0 m depth band come from two different Natural Earth datasets, each simplified on its own, so they do not follow exactly the same line. At screen size that is invisible; enlarged, the two edges part company here and there.

What it costs to look at

About 325 MB, nearly all of it the relief image, so it takes a minute or so to assemble.

The same map, built the other way

There is a second build in which the relief is not a baked image at all: the elevation model is added as a layer and GeoCanvas tints and shades it live on the graphics card. It costs 79 MB instead of 325, because the elevation arrives as numbers on a coarse grid rather than as a finished picture 36000 px wide, and it re-lights under any of the fifty projections and restyles with no request at all. It is not what this card opens because the ice sheets do not currently draw over it at the south pole, so Antarctica comes out the colour of its own height. You can preview that version if you want to compare them.