Now something different.
Off-piste snowboarding in urban or rural areas is a time-consuming hobby especially outside the mountain areas, because the best spots are neither marked nor listed in city maps. A lazy snowboarder wants to find a nice, open hillside with decent slope and sparse treeline, but finding even a few spots requires numerous trips to countless would-be locations. But hey, we have open source GIS tools and Open Data to mine for just that!
So I opened up Quantum GIS and the Raster Calculator.