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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?

PolyGeo
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Jermain Marthin
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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? http://gis.stackexchange.com/questions/119150/order-of-polygon-vertices-in-general-gis-clockwise-or-counterclockwise/147971#147971 – mdsumner Aug 27 '16 at 08:35
  • The point of simple features was to remove the ambiguity about what was a hole and was is not. Any Polygon is just one island, anything that comes next is a hole in that island. That's why you need multipolygons, one island per Polygon in a MultiPolygon. In this context the winding doesn't matter, though I think the spec is the reverse of that for shapefiles. It's interesting there's no answers here, maybe no one's really 100% sure - like me :) – mdsumner Aug 29 '16 at 01:03
  • This has already been answered here: http://gis.stackexchange.com/questions/119150/order-of-polygon-vertices-in-general-gis-clockwise-or-counterclockwise/147971#147971 – jbalk Aug 31 '16 at 03:37

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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 –  Jan 23 '13 at 19:45