In a previous article (Proc. 3rd Int. Conf. Document Anal. and Recogn., Montreal, Canada, pp. 227-30, 1995), we showed that a line sweep algorithm is an efficient means of line thinning. A line sweep is a process that works on polygonal figures and pairs the edges that bound the figure interior from two sides. In this article, we improve and extend this approach in the following way. First, a new method is used for grouping paired edges into regular and intersection regions. The regular regions can be found at the site where pairings between edges exist. Intersection regions, on the other hand, are where such relations cease to exist, due to the fact that pair relations between edges of wide distance are cancelled. Secondly, a salient feature of our new approach is to simultaneously find the set of regular regions that attach to the same intersection region. Such a set is called an intersection set. The output of our algorithm consists of skeletons as well as intersection sets. Both of them can be used as features for subsequent character recognition. Moreover, the line sweep thinning algorithm is efficient in computation as compared with a pixel-based thinning algorithm which outputs skeletons only.