Sweep

A systematic pass across a site with a locator and radar to find everything present, rather than tracing one known line. A sweep is how undocumented and abandoned utilities get found at all.

Tracing a known line answers "where does this run"; a sweep answers "what is under here". Crews walk a grid, work both passive and active modes to catch conductive targets, and run radar over the same ground for the non-conductive ones. Sweeps are what pre-dig, pre-demolition, and pre-purchase work actually consist of, and they routinely turn up lines that appear on no drawing and belong to nobody anyone can identify.