I have a mortgage plan that was given to me by the bank when I purchased my home. Can this be used as a plot plan?

The purpose of a plot plan is for determination of compliance with dimensional controls of the Zoning By-Law.  A mortgage plan is only a rough approximation of where the house is located, and was prepared only for mortgage purposes.  Due to the inaccuracy of these plans, they can only be used if the project is far in excess of the required setbacks (generally, at least 15 feet in excess of the required setback).  If the plan shows that your project will be close to the required setbacks, a more accurate plan will be required.