Soundings, plotted, never contoured

A depth contour is not a measurement. It is a line drawn between two soundings by somebody who was not there.

A hydrographic survey produces two things. A coastline, which is observed, and a set of soundings, which are measured — a depth, at a position, at a moment, reduced to chart datum. It does not produce contours. Contours are added afterwards, by interpolating between soundings that may be sixty metres apart over ground that changes in six. On a sand bar that interpolation is the difference between a passage and a grounding.

So the plates here draw one stroke each — the coast — and put every depth on the sheet as a figure. Plain figures are metres below chart datum. Underlined figures are drying heights: ground that stands above chart datum and uncovers, which is the chart convention and is the only piece of notation on the sheet.

The set as shipped. Counted out of the SVG files in public/plates/, not out of the script that drew them.
Sheet	Station	Soundings	Drying	Deepest, m	Line spacing
HR/1	Halberry Roads	175	7	23.6	58
SB/3	Skellow Bar	229	16	20.9	52
NR/2	Nethermill Reach	265	37	12.1	46
CS/1	Cargreave Sound	150	3	71.5	64
OH/4	Ossett Head	206	4	48.8	55
FN/1	Feltwater Ness	166	31	8.0	60
BD/1	Brindley Dock	340	0	6.4	44
Total	7 sheets	1531	98	—	—

The eighth station has no sheet

Marnhead Test Gauge is not a place. There is nothing there to survey, so there is no plate for it, and the gap in the wall is the honest entry. A sheet drawn for it would have been the only invented drawing in the set.

Said plainly: this seabed is a worked model

Wrackline is sold as a template and these eight stations are fiction. The coastlines and the 1531 depth figures on these sheets come out of a deterministic function in data/surveys.mjs — not out of a survey vessel. There is no random number generator in it, so the plates redraw byte for byte, and that is the point: they can be checked. They are drawings and they are not bathymetric records, and replacing them with your own survey is the first thing this template asks of a buyer. A page that captioned them otherwise would be selling a liability with the design.

All 7 sheets

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Wrackline is an aid to planning and is not a substitute for an official tide table. Do not navigate on it.