Question

say the definition of contour lines and mean sea level​

Answer 1

Answer:

Contour line, a line on a map representing an imaginary line on the land surface, all points of which are at the same elevation above a datum plane, usually mean sea level.

Explanation:

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Answer 2

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Contour Line :

➡Contour line, a line on a map representing an imaginary line on the land surface, all points of which are at the same elevation above a datum plane, usually mean sea level.

➡Imagine a land surface inundated by the sea to a depth of 100 feet (30.5 metres)—that is, the intersection of a horizontal plain with the uneven surface of the land. If then a line representing the edge of the sea is drawn on a map of the area, the result would be a contour line, and it would be called the 100-foot contour. Similar contours could be drawn at successive 100-foot intervals or at any desired interval...

Mean sea Level :

➡Mean sea level is the datum to which elevations and contour intervals are generally referred. If mean sea level were to rise 20 feet (six metres) the new shoreline would be where the 20-foot contour line is now shown..

➡Mean sea level is the average height of the sea over longer periods of time (usually a month or year), with the shorter-term variations of tides and storm surges averaged out. Eustatic (or absolute) mean sea level reflects only the change in sea height, whereas relative mean sea level represents the change in sea height and changes in the level of the land at a local or regional scale. Changes in sea height are caused by changes in water volume or mass, and by variations in the shape of the oceanic basins over geological time scales.

➡ The main factors that increase the volume or mass of the ocean are: the melting of land-based sources of ice (glaciers and ice caps, and the ice sheets of Greenland and Antarctica); thermal expansion of seawater as it heats up; and changes in water storage on land. Vertical land movements arise from both natural geological and anthropogenic processes. Natural processes include tectonics (i.e. earth quakes) and glacial isostatic adjustment (i.e. the ongoing adjustment of the earth following the reduction of ice coverage from the last glacial maximum 25,000 years ago). Anthropogenic processes usually result in subsidence, caused for example, by withdrawal of ground water...

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