Inland Water Map

What the map shows

Every cell of about 10 metres holds one of three classes of water: general water (lakes, reservoirs, ponds, marina basins, rivers, canals and the sea along the coast), streams and becks, and ditches and drains. Close in, each is drawn in its own colour, as the key shows. Any cell with water in it at all takes its class, so a stream a metre wide shows as an unbroken line of cells, and where two meet the worse is kept: a stream running into a lake is part of the lake. That is deliberate: for a landing, a cell with any water in it is a place a rocket can end up wet, and the classes let a landing tool treat a lake and a ditch differently.

Zoomed out, a pixel covers far more ground than one cell, so its strength shows how much of it is water. Open water stays solid, a river becomes a fine line and a scatter of ponds a faint wash. A pixel with any water at all in it keeps at least a trace of colour, so small water does not vanish as you zoom out.

Where the data comes from

The water comes from two sources, and a cell is water if either says so. The first is ESA WorldCover 2021, a global land cover map at 10 metres made by the European Space Agency from Sentinel-1 radar and Sentinel-2 imagery, whose permanent water class gives the same quality everywhere. The second is OpenStreetMap, whose mapped lakes, river areas, ponds, marina basins, rivers, streams and canals are drawn on top. The satellite misses water it cannot see, such as rivers in the shade of trees, crowded marinas and anything narrower than a cell; the map fills those in wherever someone has mapped them, which is most places in Europe and North America and fewer elsewhere.

Ditches and field drains are kept as a class of their own, since many are dry for much of the year and some run underground; streams and drains that pass through culverts may show as open where they are not. Out at sea there is no data here; the open sea comes from the terrain store instead. The database currently covers the whole world, United Kingdom, EU, North America, Japan and Australia & New Zealand.

Why a rocketry site maps water

A rocket under a parachute drifts with the wind, and a launch site that looks clear from the flight line can have a reservoir or a river a few hundred metres downwind. Water is one of the surest ways to lose a rocket and its electronics, and wading in after one is a risk in itself. Seeing where the water is, how much of it there is and how far away the nearest is shows where a recovery could end up wet and how short the drift has to be kept.

The same water data is going into the Altimeter Cloud Landing & Radio tool, alongside the trees and the ground, for the chance of a landing in water before anyone flies.

Use the data in your own projects

Everything on this map is available through the free Inland Water API, no key needed: any square up to 30 km across around a point, every cell as its water class in two bits, all three classes or just those you ask for, uncompressed or packed with zlib or LZMA. The download panel on the map does the same thing from here: put the cross on your site, choose the size and compression, and save the file.

The file uses the same 32 byte header as the tree canopy and roads files, with two bits a cell, four cells to every byte. Before compression, near Windermere (54°N):