Sorry but the police want the blueprint of your home in case they need to perform a no knock raid. Please provide it or you will be fined $100 per day.
You typically have to pay for it, but it is not particularly expensive. It's part of the process if you plan on buying a property, in order to ensure everything is up to code, property lines are where you expect them to be, etc.
Unexpected easements can be a real bitch if you buy a property only to find out part of it isn't actually yours, or that it is technically infeasible to update or rebuild a portion because of an undocumented/illegal code variance.