Automatic Contour Labeling
Mathematica automatically chooses appropriate levels for contours, and automatically places labels in readily readable positions.
In[1]:=  |  ContourPlot[Sin[3 x] Cos[x + y], {x, 0, 3}, {y, 0, 3},
ContourLabels -> Automatic, ColorFunction -> "Pastel"] |
Out[1]=  |  |