Contour Maps Explained
Contour lines help geologists (as well as hikers) understand
the slope of the land. Each line represents the elevation at that line.
If you were to walk across a line, you are changing elevation. The steeper
the slope, the more lines you will cross in a short distance.
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This concept of contour lines also works under ground. Just like rocks above ground can be seen to be bent, forming anticlines (domes) or synclines (saddles), these structures extend beneath ground. Therefore, if the geologist understands what the structure of the layers of rock underground look like (either by well data or geophysical evidence such as seismic reflections), he or she can draw a contour map which represents this structure |
Above ground, contour lines represent elevations, or heights.
Below ground, the numbers represent depths BELOW the surface. Therefore,
a 1,000 meter contour line equals a depth of 1000 meters (or NEGATIVE
1,000 meters), and would actually be higher than the 2,000 meter contour.
(To be more accurate, generally, subsurface contours are mapped relative to a SEA LEVEL datum, so even below the ground's surface you can have positive contour values, and only get negative values when the contour depth is below sea level. ---- thanks, Paul!)
