converting polygons to lines flips direction

[JaroslawSobanski]

Hi All,

What I want to ask about is not really an issue but I would like to understand why such thing happens.

I'm using ArcGIS Desktop 10.0 SP3. I have two shapefiles: polygons and polylines. Both added to ArcMap as single layer each. Imagine I digitize two not complicated polygons. One I digitize clockwise, the other one anti-clockwise. Then I select, copy and paste them to polyline shapefile which essentially means converting them to polylines.

Why the direction of both polylines is like they have been digitized clockwise?

I mentioned the first "clockwise polygon" only to emphasize that it's not a random thing and they're not getting "flipped" - just those polygons digitized in anti-clockwise manor. Why is that?

Regards,
Jarek

[DuncanHornby]

Jarek,

I think its to do with correct topology of the polygon. If you look at the Help on the Check Geometry tool it mentions what direction an outer ring a polygon should be. I guess when you copy the polygon into the polyline featureclass ArcMap is enforcing correct topology for the polygon and consequently your polyline ends up clockwise. Well thats my guess of whats going on...

Duncan

[JaroslawSobanski]

Duncan,

Thank you for your response.

I just realised that polygons get converted to that correct form right after I finish drawing them. Same with inner rings. So it has nothing to do with converting them to polylines.

Regards
Jarek

[DanLee]

The counter-clockwise "ring" is reserved for polygon holes or "inner rings". When you digitize only one ring to finish a polygon, it is automatically considered as the outer ring and corrected to be clockwise.