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canyon_height = 50.0 (default)
canyon_width_x = 50.0
x
z
y
canyon_wall_left (if canyon axis oriented in y-direction,
otherwise use canyon_wall_south)
(default; use if canyon axis
oriented in y-direction;
if canyon axis in x-direction,
use canyon_width_y)
topography = 'single_street_canyon'