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209 Dense boulder field

ISOM 2017-2
209 Dense boulder field (ISOM 2017-2)

Geometry: area.


An area which is covered with so many blocks of stone that they cannot be marked individually and the runnability is affected, is shown with randomly placed and orientated solid triangles with sides of ratio 8:6:5 (inner angles: 92.9, 48.5, 38.6).

A minimum of two triangles must be used.

A minimum of two triangles should be used. One triangle may be used if it is combined with other rock symbols (for instance directly below cliff symbols (201, 202), adjacent to boulder symbols (204-206) or combined with stony ground symbols (210-212)).


The maximum distance (centre to centre) between neighbouring triangles: 0.6 mm.

Density: 2-3 symbol / mm2. To be able to show obvious height differences within a boulder field, it is permitted to enlarge some of the triangles to 120%.

Footprint of individual triangle: 12 m x 6 m.

Colour: black.

Correct examples