Plotting anything on a map instantly makes it interesting.
Rentonomy's famous 'square' map of London is particularly useful for displaying area-based demographic nuggets of gold: http://www.rentonomy.com/maps/discover
Illustreets (http://illustreets.co.uk/), organiser's of this event, have taken things a step further (in a similar vein to previously featured Datashine: http://www.realpundit.com/home/2014/datashine-by-oobr-puts-uk-census-on-the-map-warning-not-safe-for-property-porn-addicts).
And the (was going to be privatised, now isn't) Land Registry, which holds every registered deed and lease in the UK, has taken on the baton to make as much of its data openly accessible as possible. They certainly lead the API charge, but have a long way to go in making data available sooner rather than later.
Read more about the event here: http://blog.landregistry.gov.uk/using-open-data-map-future/
and check out the #opendata hastag: https://twitter.com/hashtag/opendata?src=hash