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In an article titled 'How does Google Earth work?' Nature says that under normal circumstances downloading the kind of high-resolution 3D images and zooming in on them in the way that Google Earth can would take something like 69 years on the fastest Internet connection.

Using technology it acquired in 2004 with the purchase of software company Keyhole, Google maps the earth into tiles.

'As you zoom in, the computer explodes each tile into smaller sub-tiles, each with higher resolution, and re-forms the polygon into a ball,' Nature explains. 'The process continues as you zoom. This means that the virtual globe only has to download high-resolution data when the viewer is actively zooming towards it.'

The technology has also been applied to Google Moon, a work in progress.