It is indispensable to acquire geographic information from the existed topographical maps with various scales in the process of establishing geographic information system. The hatched polygons

which represent residential areas

are one of the most important sorts of map information. The strategies and algorithms of recognizing and extracting hatched polygons based on scanned map images are put forward and discussed. The RLS transformations in four directions for segmenting the hatched polygons are developed and realized. In addition

the algorithms for image transformations such as shrink

expansion

thinning

open graph deletion and hatched polygon recognition are also discussed in detail. Experiments show that recognition rate is about 96 percent with the methods developed in this paper.