A reference book I have states that (e.g.) "70% of France is less than
600 metres above sea level".

How could I check the validity of *such a statement* (not necessarily
*that one*) without resorting to relief maps in atlases or other
manual methods?

How could I produce similar statistics for other countries or regions,
heights, and so on?  E.g. "90% of the Netherlands is below 200m" or
"40% of Texas is above 300m"?



Question is for interest only.  Don't spend hours of your life on it. 
No specific data for the sample questions is needed, although if such
staements about the UK can be found, that would be interesting.