Of all that differentiates Charlton from MLJ, nothing separates the two comic lines more than their fictional cities. Oh sure, each publisher had a few psuedo cities wherein their characters visited from time to time, and even a bigger light real metropolis like New York is referenced on occasion. However, when you think of each, you think of Hub City and Riverdale.
The first of the two to appear was Riverdale. Originally referred to in Jackpot Comics #5 (Spring, 1942) in relation to Riverdale High, wherein Archie and his friends attended, this locale soon grew into a life of its own. Reflecting the rather comical but upbeat sentiments of its prominent citizens, this town's actual place on the map has ever been ascertained. Having beaches yet snow, plains and mountains, large buildings and small residential communites... it was a study in contrasts.
While there was a Riverdale both on Earth-MLJ, the world that had a golden age Archie and gang occasionallly rub elbow to elbow with such World War II heroes as the Shield and Hangman, the modern day Archie's Earth also had its own variation of the busy burg, occasionally attracting the attention of Pureheart the Powerful and the Punisher... yes both Riverdales drew the noble champion and grim guardian to its city limits.
As for Earth-Four, Hub City was that planet's Gotham City equivallent with such heroes as the Blue Beetle and the Question protecting it from the vile elements of civil vice. Not as much has been revealed of this population centre aside from its tendency to draw costumed crooks to prey upon the innocents. Eventually, even Captain Atom and Nightshade left the confines of Washington, D.C. to assist their fellow Sentinels in protecting this hub of hubris. Although nothing could protect it from the Crisis that was to come.
An interesting aside... the real cities upon which these two were (undoubtedly) unintentionally inspired by have far more fascinating stories yet to tell...