kaulike writes "The European Space Agency's GOCE satellite, launched in March 2009, has provided a spectacular, highly detailed map of our favorite gravity well. This map shows the normalized surface of the earth as defined by gravity, showing the relative altitude differences from the average for each surveyed point. The article provides the helpful metaphor that a ball resting on this surface would not roll anywhere, even though there would be visual slopes, as gravity is equalized across the globe. There is a fascinating deep area in the Indian ocean (-100M) and a high area near Iceland (+80M), proving conclusively that our world is not homogeneous in terms of density (or practically any other measure). Does anyone know whether these anomalies correspond to known geographic phenomena? Deposits of heavy metals perhaps, or hotspots where the mantle is thinner? I know little about geodetic stuff, but I'm curious about the reasons for wrinkles in the data set."