The Urban Fabric of English Cities
I created this image using the buildings layer from Ordnance Survey's Open Data VectorMap District product.
All that's shown is building footprints for eight English cities, plus London. For the eight smaller English cities only those areas within the official city limits are shown (i.e. not the entire metro area).
I created this in QGIS 2.4 and exported from the Print Composer. There is a much higher resolution version available below - I turned this into an A0 print, which hangs on the walls of the Sheffield GIS lab.