It depends ono what you want to do. 0
The fft function does not care what the units of the independent variable are, so they can be time, distance, pixels, or anything else, so long as they are regularly-spaced in tthe vector.
The fft2 function could be appropriate here, since it will take the Fourier transform in two dimensions. The same constraints apply as to element spacing regularity. See the documentation for relevant details.
