"How boring would the world be," asks Simon Garfield, "if we knew precisely where everything was?" Simon reflects on the many mistakes and deceptions in some of our best-loved maps. He begins with the map of the London Underground where lines on the map bears little resemblance to reality but is "informationally brilliant". He talks about California, the subject of a "sustained cartographic foul-up": for 200 years it appeared on maps as an island, and it continued to do so even after navigators had tried to sail all the way round it - and failed. And then there's "one of the great phantoms in the history of cartography" - the Mountains of Kong. They were apparently a wide central mountain belt that in the eighteenth-century appeared to stretch across thousands of miles of West Africa. Despite being repeated on map after map for almost a century, however, they were a pure figment of imagination. Simon celebrates these mistakes, describing them as the "accidental discovery...of searching souls". In these days of digital maps, he hopes that we can still find "strange and charming and wonderful things - mountains that don't exist and islands of the imagination". Producer: Adele Armstrong.

The geographer and polymath Jared Diamond argues that apparently slight differences in geography can have profound consequences for the culture and history of nations.

Jerry Brotton, Professor of Renaissance Studies at Queen Mary, University of London, argues that how we see the world depends on where we stand on it. He takes us back to the Hereford mappamundi - with its unicorns, griffins, cannibals and fabled cities - a world picture completely consistent, logical, and comprehensible to the England of 1300. Google Hereford today, Professor Brotton says, and you find "a very different set of digital preoccupations"; not Babel or Jerusalem but how far we are from Hereford's Cider Museum or the nearest bike shop. He concludes that "each period in history gets the map it deserves, whatever version of salvation it offers". Producer: Adele Armstrong.

Tim Harford returns with a new series of Pop Up Ideas. This time Tim and his guests tell intriguing stories inspired by maps. In the first talk, Tim argues that maps - for all their beauty - can be dangerous. In the hands of powerful people, the map begins to shape the world in its image. He tells the story of th Johann Gottlieb Beckmann, who mapped German forests. He developed the idea of the "normalbaum", a kind of platonic ideal of what a tree should be, which could be planted in neat rows to make mapping and harvesting them easier. It appeared to be a brilliant idea and produced unprecedented growth in the forestry business. But the forests came to resemble the map - with all its uniformity - and eventually the resulting lack of diversity led to the destruction of the forests themselves. Tim then looks at the taxpayer-funded Home Owners Loan Corporation (HOLC) which operated in Depression-era America and refused "to grant credit to people, not because of their credit history, not because of their ability to repay, not even because of their need. But just because of where they lived on the map." Producer: Adele Armstrong.

Tim Harford presents the last in the series, 'Pop-up Ideas'. Tim explores the concept of 'The Tragedy of the Commons' - a term coined by the American ecologist Garrett Hardin in a hugely influential 1968 essay. He compares Hardin's work to that of the American political economist Elinor Ostrom, to reflect on the impact of mankind on the world around us. Producer: Adele Armstrong.