[an error occurred while processing this directive][an error occurred while processing this directive]
July - September 2003
The difference between the major and minor axes of the WGS84 ellipsoid is 42,770 meters. The difference between the length of the radius at the equator and one of the poles is 21,385 metersonly 0.33 percent of the radius. The "flattening" of the earth is, geometrically speaking, relatively insignificant but in terms of geography, it has a tremendous impact.
If the Earth Stood Still
What would happen if the earth stopped spinning and the centrifugal effect ceased to force oceans to accumulate around the equator? It appears that the world's ocean would split into two polar oceans and leave the equatorial area totally dry. To model this hypothesis, a value of 6,371,146 metersthe distance from the earth's center indicates the approximate elevation of the sea level on the reference ellipsoidwas specified to separate water from land. For this "what if" simulation, the elevation of the sea level was based on the assumption that the volume of ocean water would be about the same as it is today.
Returning to a geoid representation of the earth, one more simulation models an earth where all the glaciers have melted. This simulation might predict a future that is only a few hundred years distant if the large glaciers of Antarctica and Greenland, which currently cover approximately 10 percent of all land, melted as a result of global warming. If all the water in these glaciers were released, the MSL would rise about 80 meters above its current level.
GIS makes it possible to explore the effects of different conceptualizations of the earth's shape and model a variety of global conditions.
The author would like to thank his colleaguesMelita Kennedy, Lenny Kneller, Corey LaMar, and Marcelo Villacresfor their significant contributions to this article.