The effect of sea-level rise on Great Britain

Question P7.2.5

The mean altitudes of the 10 km $\times$ 10 km hectad squares used by the United Kingdom's Ordnance Survey in mapping Great Britain are given in the NumPy array file gb-alt.npy. NaN values in this array denote the sea.

Plot a map of the island using this data with ax.imshow and plot further maps assuming a mean sea-level rise of (a) 10 m, (b) 50 m, (c) 100 m. In each case, deduce the percentage of land area remaining, relative to its present value.