Launched in July 2005, Google Earth (earth.google.com) has become familiar to many Earth scientists.  Some, like me, may have needed encouragement to try it out. Whatever, once up and running on a modern PC with Windows 2000 or XP and broadband connection, even the free version of the software that you need to access Google Earth is compelling, even addictive.  It takes no more than a few minutes to realise that it revolutionises teaching of many aspects of Earth science, and will be used too as a top-line research tool by anyone interested in spatial data.

Based primarily on natural-colour images that cover the entire Earth, much at Landsat TM 15-30 m resolution but for some areas using other images that resolve to the order of a couple of metres or better, Google Earth also uses global topographic elevation data. This is where it takes on its revolutionising role.  It is easy to view the surface of any part of the planet in oblique perspective, when all topographic and a great many geological features show up dramatically. It is the ultimate ‘Swiss Hammer’ – mapping the complex geology of the Alps was only possible by viewing exposures in one massif from the vantage point of another. Choosing appropriate zoom factors connects geological features that are on different scales. Design of the database – it is perfectly seamless, except where resolution changes in mostly urban areas – makes it possible  at broadband connection speeds to roam in real time at any scale. This allows you to simulate flight at any altitude and with any downward look angle: ‘grand tours’ to visit all the famous geological sites you have longed for on every continent become simple. The novelty of 3-D simulation also means that there is much to discover.

Sometimes, even in one’s homeland, it is possible to get lost, especially at large scale. By turning on GIS layers for rivers and roads (in many areas populated places, even street names and fast-food outlets show) navigation is made easier. It is the linking of images with other kinds of data that gives Google Earth its potential for research power. Designed as an easy-to-use geographic information system, by purchasing professional versions of some GIS software you can add layers interpreted, almost literally, ‘on the fly’ (Butler, D. 2006. The web-wide world. Nature, v. 439, p. 776-778).

An immediate attraction, both for globe-trotting geoscientists and, more importantly, people engaged in disaster relief, is the way Google Earth makes it easy to become familiar in moderate detail with the terrain that has to be faced. Solving problems of access, assessing where assistance may be most urgently needed is helped enormously by its highly realistic geographic visualisation. Of course, it cuts down the need for very expensive helicopter reconnaissance.  Google Earth has already proved invaluable for assessing the aftermath of the October 2005 earthquake in Kashmir. Google facilitates the mosaicing of new images of disaster areas, such as those struck by Hurricane Katrina, and their incorporation into the Google Earth database (Nourbakhsh, I. 2006. Mapping disaster zones. Nature, v. 439, p. 787-788).

A few people get frightened by some of the highest resolution images that are available – even the lines on tennis courts show up – as if their privacy was being invaded. More seriously, some governments worry about security implications of anyone being able to see intimate details of airfields and ports.  That is silly – at any time the Quickbird or Ikonos satellites can take a snap of any part of the planet at up to 65 cm resolution for anyone who has the cash to pay for its acquisition; most likely intelligence agencies and military strategists. Privacy, at least from several hundred kilometres above, is a thing of the past.  Every geologist would like to get one-metre resolution images of their research areas. If they see something intended to be hidden for one or another reason, they have an obligation to be discrete.