Britain's green spaces have been massively degraded, the president of the Royal Geographical Society (RGS) has said.
Although more than 98% of Great Britain has not been built on, farming for wind and sun and the planning of motorways and heavy utilities have changed the natural environment, geographer Nicholas Crane added.
He said the landscape imagined by historian William Hoskins in his seminal writing of the 1950s had changed dramatically.
Mr Crane said: "The real problem we are facing is not that we have not got lots of green space left, it is that it is massively degraded in terms of quality. So a lot of our green space is not very useful.
"We are farming now for wind and we are farming now for sun as well as for crops so the countryside has changed so green space does not mean the kind of green space, the countryside that (William George) Hoskins imagined for example back in the '50s, would have regarded as green space when he wrote The Making Of The English Landscape."
Mr Crane has recently written a book entitled The Making Of The British Landscape which ranges from the Ice Age to the present. His Bafta-winning BBC Two TV series Coast has been hugely successful.
The broadcaster told a meeting of the RGS's Northern Ireland branch the definition of a green space had changed.
"It is massively degraded. I personally think the real imperative now is to improve the quality of this majority of green space that we have.
"It has a lot to do with looking after the soil quality, because we are growing crops on it, thinking very hard about building on green field sites and improving access to green space and taking care of things like run off and erosion."
As part of the Campaign to Protect Rural England, he previously argued that building on green field sites in the countryside - remote from jobs, services and public transport hubs - was no solution to the needs of an expanding population.
"It's not a sustainable, or a resilient, option. "
He added: "It's time we revalued urban living as one of our most environmentally-friendly habits.
"Urbanisation is a positive trend; it minimises our impact on the planet.
"'Density,' as the UN Population Fund put it recently, 'is potentially useful.'
"Public transport, shared housing, jobs and so on are more available in towns and cities than they are in villages. Urbanisation concentrates human impacts into confined areas, with lower per capita carbon footprints."