Double decker buses are great to gather mapping data. Just make sure you managed to grab the front seat on the upper deck, wish that the bus driver travels at a slow pace, gather all the data you think you want (and somehow piqued the next seat passenger about your slight eccentricity) et voila!
It's been a year plus, and I'm still mapping that map data...
And yeah, while fixing Meta's machine learning data along the way too. That's from 3+ years ago. At least Apple Data Team isn't making it worse over this part of the world. Fun.