Plot Plans, also known as Site Plans or Certified Plot Plans, are surveyed plans that show the buildings on your lot. The Building Department has required the filing of certified plot plans for new construction since 1988 and for additions and renovations since 1995. There may be one on file in the building department.
Another source is your mortgage company. Part of the closing requirements usually include the requirement to produce a plot plan. This may be found in your closing papers or with your mortgage company. There is no legal requirement to record or file plot plans. Please note some plot plans for mortgage surveys are "TAPED" surveys and may not be accurate enough for determining lot lines.