Leonardo represents Campi Bisenzio on map RL 12685 (Windsor Castle), and mentions it in Madrid Ms. II (f. 23r) and on map RL 12279. He planned for the water of the Bisenzio to traverse the navigable Arno Canal, in the plain between Florence and Pistoia, where Campi Bisenzio constituted a reference point, close to the "Vincian locks" on the Royal Canal. In one of the folios of anatomical studies (19106v, dating from 1508-1510), Leonardo also notes experiments on the analogy between hydraulics and acoustics. In particular, he writes of an experiment to be made at home, based on observations of a cask at Campi Bisenzio: "You will have heard that, in the portion of a wave of air that passes through a narrow opening, a human voice is closed in, as I saw at Campi one that was closed into a cask open at the bung-hole" (an opening made in the barrel at the point of its maximum diameter, where the bung is inserted).
Pistoia, a city of art, whose diocese also included Vinci, undoubtedly influenced Leonardo, who could see here famous works such as the sculptures of Nicola and Giovanni Pisano and cycles of frescoes such as those in the Tau chapel. His aunt Violante and her husband Simone di Antonio lived in Pistoia, as well as several of Leonardo's friends (mentioned in the Codex Atlanticus). These were the years when Verrocchio was working in the Cathedral ("The Forteguerri Cenotaph", the "Madonna di Piazza" with Lorenzo di Credi) and, probably, in San Domenico (where the fresco of "San Girolamo" recalls the "Baptism", fruit of the collaboration between Verrocchio and Leonardo, now in the Uffizi). Leonardo mentions Pistoia several times in his studies for deviating the Arno through Prato and Serravalle Pistoiese, in the Codex Atlanticus, in Madrid Ms. II (also with the itinerary from Prato and from Poggio a Caiano to Villa Basilica and Lamporecchio, and with topographic calculations and cost estimates) and in RL 12685 and RL 12279, as well as on the hydrographical map RL 12277. To the Diocese Museum have been brought works of religious art from the territory of Vinci (in particular from the church of Santa Maria a Faltognano), which Leonardo almost certainly saw in his youth and during the periods spent in his native land.
A centre of art and commerce, located in the vicinity of major thoroughfares of communication and rich in industries, Prato was one of the focal points of Leonardo's project for deviating the Arno; the city thus appears on numerous maps (RL 12277, RL 12685, Codex Atlanticus and Madrid Ms. II). Several of Leonardo's friends, such as Filippino Lippi, came from Prato. The works of Donatello and Sangallo found in the city, as well as the fortifications and the textile machines used in the Prato manufactories, were undoubtedly of interest to Leonardo the sculptor, architect and technician.