I had a delayed reaction to your previous mention of the title "Viscount Belgrave" - by which I mean, after I posted earlier in response, I suddenly remembered the existence of "Belgrave Square" - also of course in Belgravia. Which also contributes to your observation about the wide use of titles, family names and country estates being attached to the streets, places, terraces and squares of the city. Although I suspect the Grosvenors nowadays may be among the last of the great families to retain actual proprietorship of such original city holdings.