用一个不规则多边形擦除另一个多边形，不想用Erase工具，用接口如何实现？

【解决办法】：
可以使用ITopologicalOperator.Difference方法。
1，将被擦除的IPolygon转为ITopologicalOperator，用来擦除的IPolygon作为Difference的参数传入，返回的IGeometry即为只属于第一个IPolygon而不属于第二个IPolygon的部分。
2，将获取到的IGeometry重新赋予第一个IPolygon对应的IFeature，保存即实现了擦除的功能。

IMap map = axMapControl1.Map;

IFeatureLayer pFeatureLayer = map.get_Layer(0) as IFeatureLayer;

IFeatureClass FC = pFeatureLayer.FeatureClass;

IFeature fea = FC.GetFeature(1);

IPolygon poly = fea.Shape as IPolygon;//被擦除的IPolygon

IPolygon polyCut = FC.GetFeature(2).Shape as IPolygon;//用来擦除的IPolygon

ITopologicalOperator topo = poly as ITopologicalOperator;

IGeometry geo = topo.Difference(polyCut);

fea.Shape = geo;

fea.Store();