为了既能去除彩色城市交通地图的噪声，又能保持有用信息不致损失，在对彩色地图进行像素分类、聚类的基础上，提出了一种基于外延特征的栅格地图噪声去除新算法，该算法首先以所处理的噪声像素为原点建立一个极坐标，再通过8方向搜索来获得噪声像素的外延特征；然后按照“无偏”聚类准则与“有偏”聚类准则，确定该噪声点对道路或区域的新聚类。实验结果表明，该新方法不仅完全去除了地图中的噪声，而且使区域和道路界限分明。

This paper proposes a new procedure to erase noises on raster map. Basing taxon and clustering of color map pixels, and by establishing a polar coordinate system with its origin on any noisy pixel and searching along all eight directions till road pixel or area pixel is found, of course, sometimes neither road pixel nor area pixel is found because pixels from origin to edge of map along some direction are all noisy pixels, the number of road pixels, the number of area pixels and the number of edges at all eight directions can be abtained. Letr denotes the number of road pixels,adenotes the number of area pixels andedenotes the number of edges.r,a andeare called the character parameters of noisy pixels. Then by comparingrwitha, the character of any noisy pixel can be extracted. With“equity”clustering rule, most of noisy pixels can be clustered and grouped into either road or area. Then with“partial”clustering rule, the limitrophe noisy pixels, which can not be grouped into either road or area, can also be grouped into either road or area. At last,all noisey pixels can be grouped into either road or area. This new method can completely erase the noises on raster map, so as to obtain more effective identifying with all roads and areas on a map.