Overlap
Overlap turns up in 2 fields: geosynthetics, hydrography. Here is what it means to the people in each one.
Overlap in geosynthetics
Width by which neighboring rolls of geotextile, geogrid or GCL lie over one another to keep a continuous layer.
Unseamed geotextiles depend on overlaps that grow as the subgrade softens, from about 300 mm on firm ground to a meter or more, or sewn seams, on very soft soils. GCL overlaps are typically 150 to 300 mm with added bentonite. Fill is spread in the direction of the overlaps so the top roll is pressed down instead of peeled back.
"Overlap is two feet on this soft stuff, and push the stone in the direction of the laps."
Overlap in hydrography
The share of each swath that is also covered by the neighbouring line, planned in to guard against gaps.
The shared strip between adjacent swaths, usually expressed as a percentage of swath width. Multibeam surveys often plan 10 to 25 percent overlap so outer-beam noise can be trimmed and small steering errors do not open gaps. Side-scan surveys built for 200 percent coverage set line spacing equal to the range scale, so adjacent swaths overlap by half and every point is imaged twice. Overlap also gives a quick quality check, because adjacent lines should agree in the shared strip.
"Bump the overlap to 25 percent over the rocky stuff, the outer beams are getting chewed up."