What do we mean by "urban"?

I was reflecting on our understanding of 'urban' during my number 77A bus journey out to see Hassett + Ducatez's Brookfield community centre in Tallaght last week.The journey itself was a sort of derive as the bus crawled through the Liberties, Crumlin, Walkinstown, Greenhills Industrial Estate, over the M50 and into Tallaght before heading out to Brookfield. Once you leave the liberties you are in an urban Ireland that is outside the cultural space of architecture with a capital A. There is a huge amount of building and development but very little that is known or has been studied. There appears to be very little by way of civic infrastructure.

When I came back I searched around and found this table on a german website of population statistics:

Ireland; Principal cities:

Dublin - population = 506,211
Cork - population = 119,418
Galway - population = 72,414
Tallaght - population = 63,978
Blanchardstown - population = 62,976
Limerick - population = 52,539
Waterford - population = 45,748
Clondalkin - population = 43,879
Lucan - population = 37,424

(Source Census 2006)

On wikipedia I found out that Tallaght is seeking to be recognised as a city but has not yet succeeded in getting sufficient support - it requires an act of the Oireachtas.