None of this work would have been possible without open data from Companies House or the open data registers produced by our friends at the UK Government Digital Service. The registers ensure that we are linking public sector buyers to their exact unique identifiers that are used across GOV.UK systems.  Without these unshakeable foundations we would not be publishing such a map! The supplier data of course comes from the public bodies themselves either as open data or as privately held data.
The compliance and non-compliance data is gathered and checked by our intelligent agents, lovingly dubbed "TISCbots".
We are incredibly lucky that the UK has a very proactive open data movement within UK Government and it's civil society partners (including the Open Government Network and the Open Data Institute). The Data Strategy for the UK is led by DCMS and we contribute to this via our seat on the DCMS UK Digital Economy Advisory Group.