Interactive BAG viewer
Set background opacity
The second slider will adjust the opacity of the background map.
For more info:
Note that not all areas are generated, this will happen on the fly, but that might be slow. So be patient!
Also the data is not always accurate, it does typically have the wrong construction years for buildings older than 1850. If the year is properly set to unknown it will show up on the map as a black building.
Final not it does not work in Internet Explorer; version 9 does have canvas support but is very very slow, older version don't have canvas support apparently.