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A contour with inward ticks, marking ground that falls.
Also known as: Hachured contour, Hollow contour, Depression marking
A closed contour with short ticks pointing inwards marks a hollow rather than a hill. Without the ticks a crater and a summit are drawn identically, which is why the tick is one of the highest-value marks on a topographic sheet.
Marks a closed contour enclosing ground that falls rather than rises, using short ticks pointing towards the low ground.
Contexts: Maps
Resolves an ambiguity the contour system cannot otherwise express: a closed ring around a hollow and one around a hill are the same shape.
Contexts: Maps
A closed curved line with short straight ticks projecting from it towards its centre at regular intervals.