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How to read it

There is no coastline on this map, no land colour and no borders. What you see as the outline of Australia is only its water: every river, stream, lake and reservoir the national survey maps, and nothing else. The coast shows up because that is where the rivers end.

Dark lines and dark areas hold water all year. Paler ones hold it only some of the time, after rain or in a wet season. Thicker lines are the rivers the survey ranks as major, thinner ones are minor streams.

What it shows well

How much of the continent drains nowhere. The great salt lakes of the interior, Kati Thanda-Lake Eyre, Torrens, Gairdner and Mackay, are where much of the inland water goes and then dries out, instead of reaching the sea.

The Channel Country. In the south west of Queensland, Cooper Creek and the Diamantina spread into wide braided channels that fill only after heavy rain far upstream. They appear as broad pale bands.

Where the water actually is. The dense, dark networks cling to the east coast, the tropical north and Tasmania. Most of the rest is pale: water that comes and goes.

Where it misleads

Dense is not wet. The desert interior is covered in stream lines, because dry country still has channels. Most of them carry water for a few days in a year, if at all. The pale colour is the only signal of that.

The smallest streams are left out. Drawn in full, the minor intermittent streams would cover the continent in solid blue at this scale: there are over three million kilometres of them. So the first and smallest branches of that network, the headwaters, are not drawn; everything from the second stream order up is. The national dataset has no stream order of its own, so it was worked out from how the lines connect. Every other kind of watercourse is shown in full.

It is a 1:250,000 survey. It is built from state and territory mapping of different ages and detail, so some regions look busier than others partly because they were mapped more closely.

What it is made of

The rivers, streams, lakes and reservoirs are Geoscience Australia's Surface Hydrology Lines (National) and Surface Hydrology Polygons (National), published under CC BY 4.0. Nothing else is on the map.

What we changed: the 3.6 million line segments were joined into continuous rivers and simplified to a level of detail that still holds on a large print; the first-order intermittent streams were removed as described above; and wetlands, floodplains, farm dams and canals were left out, because the map claims rivers, lakes and streams and nothing more. The classes are the survey's own: major or minor, and perennial or not.

The version of this map that circulates online gives no source, so nothing on it can be checked. This one can be checked line by line against the national data, and every layer in it can be opened, restyled or switched off.