A new report has revealed the extent to which Switzerland's greenbelt land is being eroded by home-building. It shows that one square metre of land is built on every second.

A new report by the Federal Planning Office shows the extent to which Switzerland's greenbelt land is being eroded by home-building. It says that one square metre of land is built on every second, and the result has been a reduction in the amount of land used for farming.

The findings reveal that almost 300 square kilometres - an area the size of canton Schaffhausen - has been turned over to contruction since the early 1980s. It means that urban areas have expanded by 13 per cent in that period.

The figures show that contruction work in the housing sector has grown much faster than the building of factories and roads.

The building boom has been most noticeable in those cantons with big cities. Geneva leads the way, with a rate of expansion three times the national average. It is followed by cantons Zurich and Aargau. But the mountain cantons of Valais and Uri have also witnessed above-average growth.

The Planning Office says tighter controls need to be put in place to rein in building work. It recommends that better use be made of derelict industrial sites, and that buildings be built closer together, thus reducing the total surface area that's built on.

"As the land is not a limitless resource, we have to use the tools available to us to ensure that future generations can enjoy a sufficient room for manoeuvre," it said in its study.

However, not all cantons are in agreement. Gilles Gardet, head of town planning in Geneva, says the figures used by the Federal Office need to be put into context: "The method of calculation used works on a big scale, but is too imprecise when transferred to a local level."

Meanwhile, the amount of farmland has shrunk by some three per cent. The trend has been particularly noticeable in big cantons with a farming tradition. These include Berne, Valais and Vaud.

The amount of rural land not used for agriculture has increased slightly, the Federal Planning Office said.

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