If you're citified, you're comfortable and familiar with being in a city. When your cousin travels from North Dakota to visit you in Chicago, she might take one look at you and declare you totally citified.
The adjective citified is often used as a put-down, a way to criticize someone for being too much a city person. If your expertise includes hailing cabs and dodging pedestrians on the sidewalk, your attempts to master cattle ranching or piloting a lobster boat might inspire the locals to call you citified. A more complimentary word to use would be urbane, which describes someone who's an elegant and refined city person.