What do the Contour Levels Produced by Matlab Function Contourc Represent
So you:


  I constructed a picture with 10 rectangles, each of which has a distinct depth starting from 0.1 ending up at 1.0


and then:


  I ran the code on 0.1 contour level 


The matlab function is doing the right thing. A rectangle of height 0.1 has a contour at 0.1.  A rectangle of height 1 also has a contour at 0.1 (and 0.05 and 0.5, and 0.9999999, but not at 1.000001).  The rectangle exists from 0 to 1 (in this case).