If the file is very large, probably the easiest way to see if your data are gridded (such that the ‘x’ and ‘y’ values repeat in a specific, regular pattern) is to plot your vectors using the stem3 function. If they appear to be regularly-spaced, you can use the reshape function to form them into matrices. Then you can use your matrices with contour.
If they are not gridded, you will have to interpolate them to be gridded matrices. See the griddata (link) function and its friends to do that.
EDIT —
If ‘M’ is your (Nx3) matrix:
x = linspace(min(M(:,1)), max(M(:,1)), size(M,1)+1);
y = linspace(min(M(:,2)), max(M(:,2)), size(M,1)+1);
[X,Y] = meshgrid(x, y);
Z = griddata(M(:,1), M(:,2), M(:,3), X, Y);
figure(1)
contourf(X, Y, Z)
axis equal
grid
Experiment to get the result you want.
