Contour calculations rely upon the idea that if you have two nearby locations with known values, that at some point between the two locations, the function must have gone through every value between the two known values.
Contour calculations are only suitable for functions that obey the Intermediate Value Theorem https://en.wikipedia.org/wiki/Intermediate_value_theorem
If your array has locations with value 4 and adjacent ones with value 1, and there is no transition area, then your array does not represent a function that is suitable for contour plots. You will need to section the array according to boundaries in which the Intermediate Values do not exist, and contour each section separately.
