OK, how does one compile street maps?
Method 1: you go around and survey the town, and draw your own map.
Method 2: you use an existing map.
In aviation, the official method is to lift it from the AIPs. The data is not directly machine-readable though, so most products get it from other sources. Pre-2006, it used to be lifted from the U.S. DAFIF but that is now closed and most low cost U.S. products shut off their European coverage when that happened. Today, you would do a combination of things e.g. a B2B deal with Eurocontrol, or maybe running off various PDF reports from EAD and parsing them, etc.
But if you get successful, lifting AIP data will draw attention. Jepp got sued for this in Australia, and did some kind of confidential deal with them, and probably with other AIP publishers who smelt money after the Australians won.