 For example, maps often provide heights for the place where a route passes over a ridge rather than for the lowest point of that pass.Finally, many height indications on these maps may be not up-to-date, while glacier and firn melt has decreased the height of both peaks and key cols, quite dramatically.For example, until 2009, the Col des Maisons Blanches which lies on the Corbassière Glacier was measured to be 3,418 m, while the more recent maps (2012) show it to be 3,404 m high.