REFERENCE_LINKS:
http://www.bcn.cat/estadistica/angles/index.htm ( for vehicular data )
http://en.wikipedia.org/wiki/Districts_of_Barcelona( for population and area of districts)
http://opendata.bcn.cat/opendata/cataleg/TRANSPORT/antiguitat-veh/ ( for downloading files)
http://www.flickr.com/photos/jortegafigueiral/2478132642/sizes/o/ (image source)