10

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?

Improve this question
7
  • Arcmap 10.1 crashes a lot when labeling a featureclass that contains polygons whose outter rings are counterclockwise.
    – Kirk Kuykendall
    Commented Jan 22, 2013 at 21:43
  • Appreciate your reply. Outter lings must be created counterclockwise. Understood!
    – Jermain Marthin
    Commented Jan 23, 2013 at 12:53
  • No, outer rings must be created clockwise.
    – Kirk Kuykendall
    Commented Jan 23, 2013 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
    Commented Jan 23, 2013 at 20:20
  • 1
    Read this? gis.stackexchange.com/questions/119150/…
    – mdsumner
    Commented Aug 27, 2016 at 8:35

1 Answer 1

Reset to default
2

Clockwise is for the exterior bounds of a polygon and counterclockwise rings denote donuts within the polygon. This is the convention for shapefiles.

Improve this answer
2
  • 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
    Commented Jan 23, 2013 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
    Commented Jan 23, 2013 at 19:45

Not the answer you're looking for? Browse other questions tagged or ask your own question.