15-minute city in 15 minutes

By now everybody should know what a 15-minute city concept is. What amenities are accessible with a 15 minute walk? What parts of a city do not do well in this regard? Much has been talked about, but how would you get this information about your own city? Uhm... Find some maps online? They are outdated and use buckets that are a bit too big for local usage. Calculate those yourself? With what? There has been nothing on Github.

Until now. Here I will demonstrate how 15-minute maps are done, which open source tools help with calculations, and what further opportunities do this new tool provide.