A method of determining locations by measuring angles to them from known points at either end of a fixed baseline. By observing the angles of a triangle, the unknown distances and coordinates of the third point can be calculated using trigonometry. Historically, this was the primary way to establish large-scale geodetic control networks before electronic distance measurement made trilateration practical.
Heard on the job
We need to set up a triangulation network across the river since we can't physically chain the distance.