I am trying to reconstruct some landscape features using the buffer option in QGIS. But, how can I modify it so it does an inward buffer, not outward?

Nothing really happens when I specify a negative value at the buffer distance. There are no buffers at all even though a new layer is shown.

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    Specify negative values. – GeoSpatialEarth.in Mar 18 '17 at 18:24
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    Can you check if your landscape layer is polygon or line? If you try Vector | Geoprocessing tools | buffer(s) with negative distance on a line layer, it produces a blank layer without returning error messages. – Kazuhito Mar 18 '17 at 23:15
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    if you shrink a line using a negative buffer distance, you'll get a null geometry (you can confirm this by adding a new field with geom_to_wkt($geometry) on the buffered layer). – Steven Kay Mar 19 '17 at 1:59
  • Not sure if you will be visiting this site, but let me try to post an answer... – Kazuhito Dec 1 '17 at 14:48

This is still merely speculation, but there is a chance you were working on a line layer.

(Especially when we receive shapefiles from somebody else, its first look may not be clear enough until we look into its layer property).

You may notice something strange when you create a buffer with positive distance, on a layer which was supposed to be "polygon".

enter image description here

But it becomes more enigmatic when you try a negative buffer on a line layer.

  • There is no error message.
  • What you see is blank map canvas.
  • Its attribute table shows records of these features...without geometry.

enter image description here

| improve this answer | |
  • Is it possible that the functionality of buffer has changed in QGIS 3.0? I seem to remember that buffers were either inside or outside lines/polygons in previous version. In my recent QGIS 3.0.2, the buffer is on both sides of the line/shape with positive and with negative buffer distance values. – user3386170 May 11 '18 at 19:58
  • @user3386170 Thanks for your comment. I quickly made a test on Fixed distance buffer (QGIS 2.18.19) and Buffer (3.0.2). Their buffer outputs (from line and polygon) are identical. Maybe the change you found has been made some time ago? I am rather new in using QGIS (or any GIS). – Kazuhito May 12 '18 at 3:08

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