Plot plan or site survey?

[Luiny Tavares]

I will be closing on a single family house tomorrow, and I want to convert it to a two family I will be adding 300sq feet of space. So as I understand it I will be needing an architect do draw up plans, then I need to submit it to the city's building department for approval. And then I can start my renovation. As I am interviewing prospective architects, one asks if I have a plot plan or site survey. This will be my first time going through this process, can anyone out there help me look in the right direction, i don't know what these things are, or how I can make this process as painless as possible.