The area where a new survey meets or overlaps neighbouring work. Hydrographers compare depths across it and report the differences, which reveal datum mismatches, survey errors or real seabed change. Junction comparisons are a standard section of a survey report; large differences either explain themselves, such as a migrating sand bank, or send the processor back to hunt for a bust.
Junction with the old survey is 30 centimetres deep across the board, check the datum before we blame the sand.
Also heard as
- junction analysis
- junction comparison
Related terms
Bust
A vertical or horizontal mismatch between overlapping lines or surveys that exposes an error somewhere.
Crosslines
Survey lines run across the mainscheme lines so the two data sets can be compared as an independent check.
Chart datum
The low-water level from which charted depths are measured, set so actual depth is seldom much less than shown.
Gridding
Turning millions of scattered soundings into a regular grid of depth values at a chosen cell size.