Within the districts established by this chapter or amendments to this chapter, there exist lots, structures, uses of land and structures, and characteristics of use which were lawful before this chapter was enacted, amended or otherwise made applicable to such lots, structures or uses, but which do not conform to the regulations of the district in which they are located. It is the intent of this section to permit such nonconformance to continue, under regulations contained in this section, until they are removed, but not to encourage their survival. Nonconforming uses are declared to be incompatible with the permitted uses in the districts involved.