This City Council site has this fascinating database of the origin of street names in Barcelona. In English, Spanish and Catalan.
http://www.bcn.es/nomenclator/english/
Paral·lel, Avinguda del
This public highway was officially opened on 8th October 1894. The name comes from the fact that the street runs along the earth’s parallel of latitude 41º22’34”, north; all be it in very rough terms from a strictly scientific point of view.