Actually, it's always been referred to that Earth and the Sol System are smack dab on the border of the Alpha and Beta quadrant. So it's the Federation that straddles the two.
Also, Romulan space needs to be somewhat close to Cardassian space. Otherwise how did the Dominion use Romulan space as a short cut to attack Federation worlds? And the Federation and Cardassians did share a border, the Maquis were born because the border shifted, and the worlds now owned by the cardassians didn't like that idea.
Also, Romulan space needs to be somewhat close to Cardassian space. Otherwise how did the Dominion use Romulan space as a short cut to attack Federation worlds? And the Federation and Cardassians did share a border, the Maquis were born because the border shifted, and the worlds now owned by the cardassians didn't like that idea.