When the ultimate textbook of geology is written, several thematic maps of the world will be cited as conclusive evidence of global tectonics. Examples would be the map of global seismicity that shows just how neatly the vast majority of earthquakes are confined to the plate margins [Simkin et al., 1989] and the map showing the ocean floor topography that has been created, mostly during the last 150 Ma of Earth's history [Smith and Sandwell, 1997]. Visionaries worked out the principles of plate tectonics on much more limited datasets, but extending the principles to understanding the geology of the most remote corners of the globe—and seeing world geology as a true global entity—demands global maps.
The magnetic “stripes” of the ocean floor and their symmetry around spreading-axes can be demonstrated on a few profiles but, so far, only for the North Atlantic and Arctic Oceans have complete magnetic anomaly maps been published [Verhoef et al., 1996]. The much more complex geology of the remaining 90% of Earth's history is preserved in the continents and uniquely revealed—even below extensive areas of younger cover—by continental magnetic anomaly maps. A magnetic anomaly map of the whole world would be a map of some significance alongside these others.