It is done like this...
[x, y] = meshgrid(-100:.5:100, -100:.5:100);
The you have to calculated the euclidean distances. I assume you want them with the origin.
z = (x.^2 + y.^2).^0.5; % square root of sum of squares (euclidean distance with origin)
surf(x, y, z);
NOTE: meshgrid(-100:.5:100, -100:.5:100) might make the resolution of the plot too high. If you have trouble viewing the plot, reduce the resolution.
Use [x, y] = meshgrid(-100:5:100, -100:5:100);