Pretty sure you'd just end up with a map of public transportation lines. All major shops have to be where people regularly pass by on their commute to work in the inner city.

This is probably very different in US suburbia, but it should be true for London and other densely populated areas.

If that happened you probably haven’t refined your whitelist of commercial businesses that would qualify a high street. It’s pretty much the same stuff nationwide.. A McDonald’s, some banks, a foot locker. Etc etc.

I don't think you know how London districts work at all.

London is old enough that it will still reflect patterns from hundreds of years ago. You get old town and villages that have been joined together with newer development. Old roads that used to be a main road and retain some of the inns and shops. Also, development can be separated by parks, walls, administrative boundaries, rivers, canals, railways, new roads etc. Often the effect will persist after those things have vanished.

Google Maps shows such 'commercial corridors' in yellow.

I agree I'm sure the quantity of Nando's, pizza express and Starbucks within a given area is a probably a fantastic starting point for a heuristic to detect this.