An intersection station is usually a highly visible landmark like a water tower or church steeple that has a position that was determined by triangulation, as opposed to having equipment set up on top of it like other stations. The "point observed" is some distinctive feature of the landmark that was sighted on and was the basis of the position calculation.
Usually intersection stations were observed during a triangulation project. In addition to measuring the angles between the triangulation stations (shown above as the solid black lines connecting the observers), additional angles were measured to intersection stations. Once the locations of the triangulation stations were calculated, the positions of the intersection stations could be determined by computing the location of the intersection of the observed lines (shown as the dashed gray lines). Intersection stations were useful for mapping and topographic study, and are generally of lower order, since there is no redundant measure of the angles from the reverse direction as there is with triangulation stations.