昨天检查一区属性发现一区图层的面积属性shape_area竟然出现了负值，想必是数据转换的时候出现了问题。今天在论坛求证了一下，感谢各位的解答。
ArcGIS默认顺时针图形为正，手工画polygon的时候不管怎么画结果都是顺时针的。所以一般负值的出现是转换过程出现问题，polygon是由ring组成的，ring则是有更小的segement（line,circularArc,ellipticalArc,beziercurve）构成，所具有方向性。
解决方法是用ArcTool中的check geometry和 repair geometry工具，上述的检查结果是Incorrect ring ordering。repair后会自动修复错误，已解决。
此外，repair工具只能修复以下五种错误：
Null geometry—The feature will be deleted from the feature class.
Short segment—The geometry's short segment will be deleted.
Incorrect ring ordering—The geometry will be updated to have correct ring ordering.
Incorrect segment orientation—The geometry will be updated to have correct segment orientation.
Self intersections—The geometry's segments that intersect will be split at their intersection.
Unclosed rings—The unclosed rings will be closed.
Empty parts—The parts that are null or empty will be deleted.
更多的错误修复参照帮助中的 How to salvage a corrupt shapefile
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