This episode we go out in the field with Daniel Raven-Ellison telling us about http://GreaterLondonNationalPark.org.uk, Matt Pennells talks about his work for http://mapaction.org, and Anna Ploszajski talks about taking the hydrogen economy to the UK's favourite music festival (http://www.ucl.ac.uk/ucell/people/anna_ploszajski).

Hosted by Martin Zaltz Austwick (@sociablephysics) with help from Thomas Oléron Evans (@Mathistopheles) and Rob Levy (@aid_complexity).