  A brief set of notes about the database design for 3D maps of dust extinction
in the WFAU Archives, which support data from UKIRT-WFCAM, VISTA and VST. The
notes also detail typical use cases, such as getting colour-excesses,
extinction-corrections, spectral energy distributions and colour-magnitude
diagrams and demonstrate the SQL queries to return data, along with examples
from VVV DR2 with bulge extinction maps from Chen et al. (2013).
