Central City is stated in the Flash/Arrow verse as being 600 miles from Star City/Starling City. Not exactly what I would call close. In the comics Star City as it is known is in California. Central City is in Missouri. However do to some Easter eggs in Arrow it appears in this universe Star City is located where Seattle would be (coordinates given in one episode places I believe it is the Glades in a neighborhood in Seattle. Also the zip code given for Star City in one episode is a Seattle zip code) they haven't stated od given hints to where Central City might be other than 600 miles away from Starling/Star City. But again back to my original point I would not call 600 miles close.