The background image for these pages is created from satellite-
derived free air gravity anomalies (gray-scale) and color
contours of the Earth's geomagnetic inclination, declination and
field strength. Satellite-derived free air gravity anomalies
Ocean surfaces represent a gravitational equipotential surface.
Free air gravity anomalies are then derived by calculating the
rate of change in elevation of this surface. The area of the
image is the central Atlantic Ocean with the Lesser Antilles
Islands and Venezuela located to the west, and Africa to the
East. The Mid-Atlantic Ridge (short north-south segments) and
related transform faults and fracture zones (generally east-
west) are well defined through the center of the area. The
Earth's gravity field is monopolar so it always points down
towards the Earth's center. But the magnetic field is dipolar,
which means that the direction of the field changes with
geographic position. At the geomagnetic poles the field is
vertical or perpendicular to the Earth's surfac