I’m in Edinburgh for the weekend. Calton Hill on a Saturday afternoon, the wind off the Firth of Forth doing what it always does — pulling slightly inland, ruffling the gorse, making you tuck your hair behind your ear for the third time in two minutes. The city is laid out underneath: Princes Street, the Castle rock at the western end, the long pale ridge of Arthur’s Seat to my back.
A jet passed overhead. High, decisive, climbing northwest — out of EGPH by the look of the angle, off to somewhere in the north Atlantic. I did the thing I keep doing, which is to open the radar.
There it was. Crisp on the trace, the icon settling on the map as I watched.
I stood there for a moment longer than I’d planned.
Somebody in Scotland decided this was worth doing
That jet’s signal didn’t reach the Dataero radar by magic. It reached it because somewhere — possibly a flat in Leith, possibly a converted attic in Stockbridge, possibly a back bedroom in Newington belonging to a retired engineer — somebody has put an ADSB antenna in the right place, run a coax through a window frame, plugged it into a Pi, pointed a feed at our endpoint, and walked away to let it run.
The result is that when I, a tourist for two days with an aviation habit, look up from Calton Hill and want to know what that jet was, the answer is there.
I don’t know who they are. I will probably never know. They didn’t sign up to be useful to me specifically. They signed up because the airspace over their city is worth being useful about, and the rest of us — myself included — get the benefit.
The receivers feeding our radar aren’t ours. They sit on rooftops Dataero will never see, run by people we’ll never meet. We point a network at what they catch. Standing here, with the Firth pulling the wind east and the city pretending to behave for the weekend, that sentence stopped being a slide and started being a real piece of Scottish geography.
What Scotland adds to the map
Coverage of European airspace is, broadly, a map of where people decided to feed. England has its rooftops. France, Germany, the Low Countries, Spain — the southern half of the continent has been busy for years. Scotland, though, is the edge of a useful coverage area for the rest of the network. A feeder in Edinburgh sees aircraft that no rooftop further south can hear as well: trans-Atlantic departures climbing out of EGPH, the Highland traffic that rarely makes it onto the mainstream maps, the North Sea rotation flights to Aberdeen. The geometry of overlap thins out the further north you go, and every Scottish antenna fills a piece of sky that nobody else can.
There is no cloud capacity that compensates for an antenna in the right city. Coverage is a function of where the people are.
So if you’re in Glasgow or Aberdeen or Inverness or Dundee with a clear horizon and a Pi gathering dust — or already feeding somewhere and wondering whether to point a second feed at us — the work your rooftop would do is, geometrically, work nobody else’s can. Open the radar and have a look at the gap; if you fancy filling some of it, the onboarding is genuinely easy.
A small Saturday note
Brothers in Arms on the headphones for the walk down, because Saturday in Edinburgh in May is the kind of weather that calls for it. A second jet passed over, southbound this time, an A320 in the descent into EGPH by the look of the wings.
Crisp on the trace, again.
Thank you, whoever you are.
— Sandy