针对GIS 平台符号库的开发过程中遇到的组合线符号偏移值非零的问题，提出了一种生成折线平行线的算 法。该算法运用向量代数简化了偏移后生成新折点的计算过程，从而提高了线要素符号呈现的效率。实践表明该方法程序实 现较简单，计算效率较高。

In order to draw combination line symbol which has an offset property value during the development of symbol base of geographical information system(GIS) platform, an algorithm generating parallel polyline is put forward in the paper. The vector algebra is used to simplify the calculating process by generating a new point set after offsetting. Accordingly it improves the efficiency of drawing line symbol. The practice shows that the method is relatively simple in programming and it has high computing efficiency.