What major city has both the longest and the shortest names? I don't know of an "official" answer, but my favorite candidate is surely:
La Ciudad de Nuestra Señora La Reina de Los Angeles del Río de Porciúncula
... in English, "The City of Our Lady the Queen of the Angels of the River Porciuncula" --- commonly known nowadays as LA = L.A. = "Los Angeles". Some sources say that the original name in 1781 was just "El Pueblo de la Reina de Los Angeles" --- not quite as long, but still a nice mouthful.
(In another LA tradition, the oldest murder mystery in the area may be associated with a woman's skeleton dating back ~9,000 years, found with a fractured skull in the La Brea tar pits ca. 1914 ...)
Actually, it might just be official. I remember reading L.A. in the Guinness Book of World Records, as "best abbreviation" or something. - RadRob