California Civil Engineering Surveying Practice Exam

The distance you measure on a map grid is not the same as the true distance on the curved Earth because projecting a surface onto a plane distorts lengths. The factor that converts geodetic (ellipsoidal) distances to grid (planar) distances is the scale factor. It is the ratio of grid distance to ground distance, so you multiply the geodetic distance by the scale factor to obtain the corresponding grid distance. This factor varies with location and projection, typically close to 1 for small areas but not exactly 1 everywhere. Resection, residual, and route survey are not used for this distance conversion; they relate to methods of position fixing, error terms, or data collection, not the distance scaling between geodetic and grid measurements.