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Is there any 'Auto-complete polygon' tool in QGIS, similar to the one existing in ArcGIS?

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up vote 8 down vote accepted

Yes, you can set snapping tolerance (e.g. to vertex and segment) you can then over digitize. A new polygon will only be created to the edge of an existing polygon. This setting can be enabled through the Settings Menu> Project Properties> General tab.

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Just an update for version 1.8.0-Lisboa: This setting was moved slightly, to Settings>Snapping Options... – ChrisHamby Apr 26 '13 at 18:53

From the Settings > Snapping Options dialogue:

Under 'Snapping Mode' choose 'Advanced'

1) Check the box next to the layer you want to 'auto-complete' to (to enable snapping)
2) Check the box under 'Avoid Intersections'
3) Check the box at the bottom 'Enable Topological Editing'

Now digitize a new polygon ensuring you are either starting and stopping the sketch inside the original polygon, or at least crossing the original polygon where you want to auto-complete your new polygon along.

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