Offsets are lateral measurements taken to the left or right of a survey line to locate details like buildings and boundaries. They can be short (<15m) or long (>15m) and either perpendicular or oblique. Obstacles to surveying include things like ponds, buildings, or hills that make chaining a line difficult. There are obstacles to ranging but not chaining, obstacles to chaining but not ranging, or obstacles to both. Plane table surveying involves conducting fieldwork and plotting simultaneously using an alidade and other instruments mounted on a drawing board. Details are located using methods like radiation or intersection.