Slough Heat-loss map

SBC have published an excellent-looking "Heat Map" of Slough here.


Constructed from thermal imaging photos in March 2008, it claims to show the level of heat loss from all the houses in Slough. Potentially a great tool, but 2 questions come to mind ...

1) just when was the data gathered? To measure how much heat is being lost, the measurement has to be taken at a time when heat is being used within the house.
2) what does the scale 1-7 actually mean? Insulation is measured in "U" units - a measure of the way heat travels through a specific area - http://en.wikipedia.org/wiki/U-value#U-value

The SBC environment team are pretty friendly, and deserve full credit for organising this, so I hope to get some context for the data, pretty though the colours are .... tools like this are going to be increasingly more important as we try to close the energy gap - it's not enough to find new ways of generating energy, we need to reduce the amount we use too.