The Nottingham Built-up Area (BUA), Nottingham Urban Area, or Greater Nottingham is an area of land defined by the Office for National Statistics as which is built upon, with nearby areas linked if within 200 metres - see the List of urban areas in the United Kingdom article for a broader definition. It consists of the city of Nottingham and the adjoining urban areas of Nottinghamshire and Derbyshire, in the East Midlands of England. It had a total population of 729,977 at the time of the 2011 census. This was an increase of almost 10% since the 2001 census recorded population of 666,358, due to population increases, reductions and several new sub-divisions. Geography Greater Nottingham is largely within the three districts of Rushcliffe, Broxtowe and Gedling surrounding the city, though the area spills into the Nottinghamshire district of Ashfield, and also to the Amber Valley and Erewash districts of Derbyshire. The Nottingham Urban Area is, by the ONS' figures, the 8th largest in England (9th in the UK), with a population size between that of the Tyneside and Sheffield built-up areas, and a total area of . The Nottingham Urban Area is bounded to the west by a narrow gap between Draycott (to the west of the Breaston urban area sub-division) and Borrowash (to the east of the Derby Urban Area). The Heanor/Ripley and West Hallam north-western extensions have a somewhat tenuous linkage through to the core of Nottingham City largely due to ribbon development, and are in close proximity to other nearby urban areas which together, almost link to Derby from the north. Sub-divisions do not always match administrative geographic boundaries; the subdivision of Clifton for example is within the Nottingham Unitary Authority city area but is subdivided by the River Trent. The Nottingham subdivision oversteps the city's borders at several locations. Together, these two subdivisions exceed the official city population (305,680 in 2011) as a result, even though West Bridgford includes the counts of city suburbs Silverdale and Wilford. In the 1991 census, Ilkeston was considered outside of the Nottingham Urban Area, and its addition gave the BUA an 8% increase in 2001. This was due to improvements in mapping methodology by the ONS, and is chiefly responsible for the increase in sub-divisions over censuses rather than any large scale 'bricks and mortar' building, as much of the area between the cities is protected green belt and wedges,