Central and Keystone cities are the twin cities protected by the Flash Family.
Keystone was the home of Jay Garrick, the original Flash and later became the home of the third, Wally West. Central City resident, Barry Allen, the second Flash, was a Central City resident who protected the city. After Jay's retirement and Barry's death, Wally took it upon himself to protect both cities from his extensive Rogue's gallery.
When the Kents are kidnapped by Mirror Master under orders from the U.S. Government, the Justice League is rallied by Wonder Woman to find him and the League head to Central City to battle and interrogate various Rogue members before learning from Captain Cold of Mirror Master's location in a villain's only bar in Keystone.
The League then heads for Keystone and successfully capture Mirror Master, stealing his tech to free the Kents from where he had imprisoned them.