What is a principal meridian?
A principal meridian is the north-south reference line used by a township-and-range survey. Range numbers count east or west from it.
Why the meridian changes the location
The same township and range can exist under different meridians. For example, T1N R1E in California is incomplete without knowing whether it references Mount Diablo, San Bernardino or Humboldt.
Canadian DLS uses numbered meridians such as W1, W2, W3, W4, W5 and W6. The US PLSS uses named principal meridians such as Willamette, Salt Lake and Sixth Principal.
Last reviewed June 2026. General information about survey systems — not legal, title, or survey advice.
Sources: US BLM — Cadastral Survey (PLSS), BLM / GLO — Principal Meridians and Base Lines (map).