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According to "ESRI Shapefile Technical Description An ESRI White Paper—July 1998", Vertices for a single, ringed polygon are, therefore,always in clockwise order. Otherwise,"Dirty" polygons occur when the rings that define holes in the polygon also go clockwise, which causes overlapping interiors.

In my understanding, you can create donuts polygon with "avoid intersection of new polygons" is checked on snapping option, even if both polygon(inner and outer) are created clockwise roated.

It has not necessary to care about clockwise rotation when you create polygon in QGIS.

Is this a right understanding?

marked as duplicate by PolyGeo Aug 31 '16 at 4:04

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  • Arcmap 10.1 crashes a lot when labeling a featureclass that contains polygons whose outter rings are counterclockwise. – Kirk Kuykendall Jan 22 '13 at 21:43
  • Appreciate your reply. Outter lings must be created counterclockwise. Understood! – Jermain Marthin Jan 23 '13 at 12:53
  • No, outer rings must be created clockwise. – Kirk Kuykendall Jan 23 '13 at 20:16
  • A bit of theory: I suspect the use of the surveyor's formula for area calculation was what drove people to adopt the clockwise convention. Clockwise coordinates produce positive areas using this formula, whereas counterclockwise coordinates produce negative areas. – Kirk Kuykendall Jan 23 '13 at 20:20
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    Read this? gis.stackexchange.com/questions/119150/… – mdsumner Aug 27 '16 at 8:35
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Clockwise is for the exterior bounds of a polygon and counterclockwise rings denote donuts within the polygon. This is the convention for shapefiles.

  • Thank you for your reply. I would like to confirm one more point. If I create three rings polygon, what should I do?? internal rings are counterclockwise. seconde one are clockwise. third ring are clockwise or counterclockwise?? – Jermain Marthin Jan 23 '13 at 12:53
  • In ArcMap, the procedure would be to create the outer polygon first moving inward while doing a union (I think?) between each step, if there are any extra duplicate areas, then you can edit them during the editing process. A multi-ring buffer will allow you to create rings about an inner polygon if you want the remaining features to be similar in shape but expanded by a certain offset distance. Hopefully I have covered your cases. An image would help – user681 Jan 23 '13 at 19:45

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