Wolfram Technology Guide: Automated Computational Aesthetics  previous | next 
Automatic Contour Labeling
Mathematica automatically chooses appropriate levels for contours, and automatically places labels in readily readable positions.
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Click for copyable input
ContourPlot[Sin[3 x] Cos[x + y], {x, 0, 3}, {y, 0, 3}, 

 ContourLabels -> Automatic, ColorFunction -> "Pastel"]
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