This paper addresses the problem of
contour line extraction from scanned topographic maps in
poor condition. A novel method is developed, using
knowledge of cartography and graphics to extract contours
by removing other layers which overlay the contours, and
reconstructing the contour lines. The contributions of this
paper are the supplementation of the use of knowledge
discovery for extraction on the scanned topographic maps.
Examples are presented from diverse applications to show
that the developed algorithm can work effectively.