Last month we had a story about hills growing into mountains and now we blog about the opposite situation…Recent press stories about what *might* happen if rising sea levels lead to a change in the datum value used for mean sea level on OS maps, has seen some people thinking that the heights of hills and mountains might be about to shrink. They are not!
We have to measure height in Britain against a commonly agreed datum level and ‘mean sea level’ is a common value chosen in many countries. It becomes the ‘zero height’ which all other heights are measured from. As land-based creatures, it’s natural for us to think of the sea as being zero height and anything above it as being ‘high’, and consequently anything below it as having a ‘depth’. So, it’s very common to see heights of hills and mountains quoted as being ‘above mean sea level’.