Abstract: A random array edge table is described as a basic data structure to form a plane chart, instead of the concepts about inner or outer rounding ring and point table. A newway that two plane geometric charts are clipped together is used to reduce the problem of two dimensional geometric modeling to the most basic problem of clipping segments. While clipping the line and arc segments with the window in a plane geometric graph, we discuss the condition of crossing, the getting of the effective crossing point and a kind of rapid way to judge the visibility about an end point on the clipped segment.