We are always suckers for data visualisation clips and this one of the northern European airspace returning to use after being closed due to volcanic ash is great. 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:
The flight data is courtesy of flightradar24.com and covers a large fraction of Europe. There are a few gaps (most noticeably France) and no coverage over the Atlantic, but the picture is still clear.
The map data is CC-by-SA openstreetmap.org and contributors.
This CC-by-SA visualisation was produced by itoworld.com with support from ideasintransit.org