A scale is usually defined as the ratio between the distance between two particular places on the map and the actual distance between the two places on the actual ground surface.
It is widely used by the geographers while studying a map, in order to explain the relationship between the map distance and the earth's distance. This scale is mentioned in the map, mostly at the bottom of the map.
For example, a map scale of 1:500000, this means that 1 centimeter on the map is equivalent to 5000 meters = 5 kilometers on the ground surface.
The reason why the continental crust differs from the oceanic crust is much different in its compositions. The continental crust is thin and less dense , is made of sedimentary and metamorphic rocks than the oceanic crust and is made of lighter elements. The tectonic plates move the composition to the rocks.
