Much of excitement about big data and visualisation bridges two ends of a complex problem, first get the data and make sense of it and then visualise it! Sourcing and combining the data is one challenge, but once you see what visualisation is when you start to realise what other data you might need. The reality is often complex and conflicted in that data sources overlap oddly or are incomplete. And as you try and combine them consistently and correct data points become more and more sparse.
Bringing open geo-spatial data together productively is a real art. One new tool developed by the Connect Places Catapult that might help is Tombolo. It combines access to a wide range of open source data and an easy walk-up use visualisation tool. Hopefully enriching a whole variety of non-technical experts in building their analyses and understanding.