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I would like to create new polygon inside the existing polygon. It does not means donuts polygon.

I would like to have two polygon without overlapping.

I can create if I don't check "Avoid intersection"from snapping option. Unfortunately, there is overlapping new polygon and existing polygon.

It must not have overlapping area.

Please tell me if it is possibele.

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If I explain very simply, I would like to create double ring polygon without overlapping. I have already create external ring polygon. I don't know how to create internal ring polygon. –  Jermain Marthin Jan 31 '13 at 22:49
    
Could you just use two polygon layers instead of one? What sort of data are you trying to create polygons from? –  giski Feb 5 '13 at 18:12

4 Answers 4

There are two ways to do it in my mind. If you have many complicated polygons:

  1. create layer with outer polygons
  2. create layer with inner polygons
  3. use Vector / Geoprocessing Tools / Difference to make holes in outer polygons
  4. merge layer from step 3 with layer from step 2 - Vector / Data management Tools / Merge shapefiles to one

Second option if you have few simple polygons:

  1. create outer polygon
  2. create hole in polygon (Edit / Add Ring)
  3. set snapping (Settings / Snapping Options...)
  4. create inner polygon by snapping to inner nodes (hole/ring) of outer polygon
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I have complicated polygons. but, second option is better for me because of simple. –  Jermain Marthin Feb 4 '13 at 21:24
    
@JermainMarthin please upvote helpful answers and accept the answer that answers your question. –  underdark Mar 7 '13 at 18:36

Use the Buffer command, with negative value i.e. -50. Operating in a UTM projection is more intuitive when using this type of action.

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Internal ring is not the same shape of outer ring. anyway, thank you for your comment. –  Jermain Marthin Feb 4 '13 at 21:25

I wonder if you might prefer to create your polygons with lines and then polygonise them with the Polygonizer plug-in? See the attached images (and perhaps also have a look at http://confound.me.uk/maps/ppv4.pdf). N.

enter image description here enter image description here

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Thank you for your comment. I have already polygon not polyline. If I start from polyline, I will follow your suggestion. –  Jermain Marthin Feb 4 '13 at 21:23
    
It is possible to convert polygons to lines in QGIS. N. –  nhopton Feb 4 '13 at 22:44

If I understand you, you have a main polygon which includes many polygons that are close. a) first draw the main polygon

enter image description here

b)Define a ring that surround all inner polygons (I am asuuming this is your case)

enter image description here

c) Make sure you have defined the snapping options as this:

enter image description here

d) Draw the first inner polygon in the ring:

enter image description here

notice since you defined that there must not be intersection of new polygons the inner polygon is correctly created.

enter image description here

e) Define the same way the remaining polygons

enter image description here

enter image description here

If the above description fits your case, that should do it.

Hope it helps

Gerardo

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