The assigned number is unique within the particular jurisdiction, and may conform to certain formatting standards that convey basic identifying information such as the property type or location within the plot map.
In the United States, APNs are typically assigned by the local taxing authority, such as the city or county within which the property is located.
[1] A parcel is an identification for taxation purposes, while a lot is a recognized subdivision of property with a written legal description that addresses permissions or constraints upon its development.
APN numbers and the property boundaries that they describe have become particularly important for the oil and gas industry with recent discoveries of recoverable hydrocarbons in the Marcellus Shale and related geological formations.
The format of APN strings can vary, it is typically a concatenation of the book, page, parcel number.