Boundary determination, redefinition and reinstatement principles
Monuments govern
The cardinal principle is that the original boundary is the line fixed by the original survey marks and plan. Measurements are evidence of where those marks were; they do not override an original monument. The hierarchy is original monuments, then original measurements, then occupation, then later surveys. Redefinition finds the original boundary; reinstatement places marks at that position.
When marks are missing
The surveyor must search for evidence: adjacent original marks, old plans, field books, witness marks, occupation and physical features. If the original mark is destroyed, the surveyor reconstructs its position from the best available evidence and records the reasoning. A boundary cannot be moved simply because occupation is convenient.
Worked example
An original corner peg is missing. The neighbouring original peg is found, and the original plan gives a bearing and distance. A fence sits 0.4 m inside the measured position. The surveyor measures from the reliable peg, checks the original plan and adjoining parcels, and reinstates the corner at the plan position, not at the fence. The fence is occupation evidence only.
Traps
Do not adopt the nearest fence; do not measure from an unreliable mark without assessing its provenance; do not treat a later plan as stronger than the original; and remember that natural boundaries such as rivers and the sea can shift with accretion or erosion, so the legal line may not be a fixed peg line.