17 April 2013
For Cornwall the figures are:
Total area of all land: 360.6 hectares
Green space and domestic gardens: 338.4 hectares
Water: 8.1 hectares
Built on: 14.1 hectares (3.9 percent)
Built on includes domestic and nondomestic buildings, roads, and railways. I have included 3.7 hectares of ‘Other’ and ‘Unclassified’ land use in that category too. Houses, old and new, include gardens; gardens of course are not built-on land.
That is the data for the whole county. In urban areas the proportion of built up land will be higher and more local land use statistics are available among the 2005 data: see here.