Hillshade — shaded relief underlay for OSM maps
Hillshade (shaded relief) is a grey halftone image that simulates shadows cast by terrain under oblique light. Hills are lit on one side and shaded on the other, and the eye instantly "reads" the shape of the surface. It is the most recognisable cartographic device for conveying relief — from Swiss topo maps to Google Maps backgrounds. OSM2CDR builds hillshade from the global Copernicus GLO-30 relief model and delivers it either as a standalone file or as an underlay beneath your vector map.
How hillshade is computed
The hillshade algorithm takes a digital elevation model and, for each pixel, computes slope and aspect, then compares them with the light direction. The more a slope faces the light, the brighter the pixel; the more it faces away, the darker. Two parameters define the "sun": azimuth (light direction) and altitude above the horizon. The classic choice is light from the north-west, 315°: the human brain habitually reads light as coming from the upper-left, and with a different azimuth relief sometimes turns inside-out (the pseudoscopic effect). A single sun has a downside too: slopes turned fully away from it degenerate into flat black patches, and whatever is there disappears. So I compute the hillshade with multidirectional light: instead of one sun, four are blended from different sides, and a slope facing away from any one of them still stays readable. The light sits 45° above the horizon.
OSM2CDR supports two slope algorithms: Horn (default, noise-robust, the ArcGIS/GDAL standard) and Zevenbergen-Thorne (more sensitive to small features). A vertical exaggeration (z-factor) is also adjustable — it boosts relief on flat terrain where an honest hillshade looks flat.
Global coverage, including the Arctic
The elevation source is Copernicus DEM GLO-30 (30 metres), an open global ESA dataset. Unlike the old SRTM clipped at 60°N, Copernicus covers all land — hillshade works for Murmansk, Norilsk, Svalbard and any polar area. Where there is no data (open ocean), hillshade is transparent rather than filled with garbage.
File or underlay
You can get hillshade two ways. First, as a standalone georeferenced GeoTIFF for GIS (opens in QGIS/ArcGIS with its own georeferencing, snaps to the right place on the map). Second, as a background underlay right beneath the vector map when exporting to PDF/SVG/PNG: you get a finished map where OSM streets and buildings sit on top of the shaded relief. Enabled by the "Hillshade" checkbox in the topographic-features panel.
Hillshade is especially striking combined with hypsometric tint (colored elevation) — the hillshade is multiply-blended into the color, producing a volumetric relief map like classic atlases. See the color relief guide.
Where it is used
- Hiking and tourist maps — relief reads intuitively.
- Background for thematic maps (density, routes) — depth without clutter.
- Geomorphology, geology, hydrology — analysis of landforms.
- Cartographic design — underlay for posters and atlases.
Attribution
The relief data is Copernicus DEM. When publishing, credit: "produced using Copernicus WorldDEM-30 © DLR e.V. 2010-2014 and © Airbus Defence and Space GmbH 2014-2018 provided under COPERNICUS by the European Union and ESA; all rights reserved" — the wording is fixed by the licence.