Expanse, amplitude, spread, stretch are comparable when they denote an area or range of considerable or conspicuous extent.
Expanse is applied chiefly to vast areas open to view and usually uniform in character.
Amplitude implies in general use an ampleness in what it describes and suggests relative largeness (as in size or range) or greatness (as in character or quality), but in technical contexts in which the word is specifically applied to the range of a variable (as wavelength or a statistical array) the notion of ampleness has given way to that of magnitude, and amplitude means no more than size or extent.
Spread is applied to an expanse drawn out in all directions.
Stretch is applied to an expanse in one of its two dimensions.