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I have to create vegetation and sensitivity maps for sites. I have a site boundary shapefile and map from raster aerial imagery behind the site boundary vector.

When I used to use Arc I used the cut polygon tool. This allowed me to create a one shapefile vegmap with different polygons that I could label according to what they are (eg: forest, grassland, disturbed areas). The cool thing about this is that it eliminated any of those slivers of areas not mapped or intersecting polygons). This is important as I need to use the map to calculate areas of each of the different vegtypes.

I cannot seem to find a similar function in QGIS. I have fiddled with snapping and it really isn't good enough. It will take me hours and hours to individually snap the vertices for a small map, let alone a huge and intricate one!

Does anyone have an answer for me to do this in QGIS?

I have not got ArcGIS Desktop and cannot do it there.

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  • It might help if you posted a before and after image from ArcGIS of what you want to achieve. – HeikkiVesanto Nov 20 '17 at 10:45
  • There is no processing, I would do the whole map like that. However, here is a picture of an example of the map I am trying to create. I do not want separate layers for each vegetation type. It needs to be one polygon. – Leigh-Ann de Wet Nov 20 '17 at 10:49
  • So are you trying to merge different layers into one? – HeikkiVesanto Nov 20 '17 at 10:58
  • No, I am trying to create one layer from the start. The cut polygons tool in Arc allows you to do this provided you start with a boundary. You then basically cut the original polygon (the whole site) into little pieces which are then labelled according to category. It is always just one polygon. – Leigh-Ann de Wet Nov 20 '17 at 11:05
  • Thank you all so much for your help! I have figured it out with your invaluable help and am now on my way to mapping up a storm. – Leigh-Ann de Wet Nov 20 '17 at 12:43
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You could use the Digitizing Tools plugin, that contains te cut-by-polygon, cut-by hand and other features like that. (go to Plugins-> manage and install plugins - > search for digitizing tools -> click install)

  • This works! Thanks so much. So I only have one more question... How do I get items I have split in the middle to be present without lines? I have tried merge but it doesn't seem to work perfectly (I have added the picture to the original question). Essentially I need to make the polygon 1 (A by product of the cutting process) merge with the larger polygon 2 so that they are one with no lines. Is this possible? – Leigh-Ann de Wet Nov 20 '17 at 12:17
  • That would be the dissolve function, standard in Qgis. If they are seperate files you might need to copy-paste the feature first. – Borgh Nov 20 '17 at 12:21
  • I have tried that, but it does not allow me to retain the map as one single shapefile. – Leigh-Ann de Wet Nov 20 '17 at 12:26
  • I have figured it out! Thank you so much for your help!! – Leigh-Ann de Wet Nov 20 '17 at 12:42
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I think you are looking for the Split Feature tool. Show the Advanced Digitizing Toolbar

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and look for the icon

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With the feature you want to split up selected you can now draw lines across it to split it up.

  • Thank you! Yes that's the one! Just one more niggling question - please see my comment in the previous answer. – Leigh-Ann de Wet Nov 20 '17 at 12:19

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