Vehicle-dependent Expedition Guide .... Edition 4.1

by Tom Sheppard and Jonathan Hanson          ISBN 978-0-9575385-4-2

Map vs Google Earth – stiff test

A section of a French Institute Geographique Nationale 1:200k map of the central Sahara compared with the Google Earth depiction of the same area (‘eye-altitude’ c.40 km).

The intuitive clarity of the satellite imagery is immediately obvious for the vehicle-dependent expeditioner, showing where you definitely cannot go, areas where it is complex and the thread of the wadis which offer a good chance of a way through. As noted on p.5.2-11, terrain type discrimination on satellite imagery – rocks, hills, sand – will be more obvious in deserts than elsewhere.

The one-minute lat/long grid is immensely useful enabling a GPS position to be plotted by eye. The IGN map has lat/long grid lines every 15’ – hence the drawn-on diagonals at the top to facilitated interpolation using pencil and dividers.

The IGN maps, put together in the ‘60s using aerial photography and teams on the ground doing astro fixes and naming peaks and wadis, is monumental cartography but its very complexity and seemingly chaotic detail makes it hard to read in examples such as this.