Similarly situated somewhere in the ambiguous "midwest" of twin worlds, Central City and Keystone City were notable as the home towns of heroes known as the Flash. The alter egos of the Scarlet Speedster, Barry Allen and Jay Garrick, were originally police scientists and gained their superspeed powers accidently. Deciding to don their crimson garb, each Flash met up with all manners of malevolent malcontents within their city's limits. As noted by Barry in the adjoining panel, subtle differences such as the lack of a Memorial Tower and sports stadium in Keystone that were located in his Central City. And no doubt visa versa. Even the parallel precincts of both cities had different architectural designs, with Central's being post-modern and Keystone's being a traditional brownstone.
When Vandal Savage emitted lightwaves on Keystone, it resonated in Central's airspace as well, and when Rainbow Raider emitted his black-and-white effect on Central, the colors from that city ended up in Keystone instead. While Central only had their Flash for a few years, Keystone's Flash was a life-long resident for decades to come.