This video is a visualization of the northern European airspace returning to full air traffic use after being closed due to volcanic ash. Due to varying ash density across Europe, the first flights can be seen in some areas on the 18th and by the 20th everywhere is open. There are a few gaps (erm, France) and no coverage over the Atlantic, but the picture is still clear.
The flight data is courtesy of flightradar24.com and covers a large fraction of Europe. Map data is CC-by-SA openstreetmap.org and contributors. CC-by-SA visualization was produced by itoworld.com with support from ideasintransit.org.