This Ichnographic map style - versus the existing common view from a hilltop maps of the day - was an incredible feat of engineering.
As per the Vox video, researchers theorize that:
"He probably used a type of disk that could measure degrees and had a little pointer to mark the angles of streets in relation to a stable point, usually North. He probably used a compass to record the orientation of the town's surrounding walls. He did this at every turn, which helped him accurately translate the walls onto paper."
As far as establishing scale, they hypothesize that he did this either by foot or with an odometer such as this.
It's absolutely incredible how ahead of its time this map was! Absolutely fascinating.
Definitely want to check out this place when I get to Florence again.