Say you have a very rectangular 2D array arr, whose columns and rows correspond to very specific sampling locations x and y. That is, the arr[i, j] entry corresponds to some measurement taken at x[j] and y[i].
Matlab’s imagesc shows you this quite meaningfully:
x = linspace(-100, -10, 10);
y = [-8 -3];
data = randn(numel(y), numel(x));