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I'm running QGIS 2.6 on a Mac, and trying to create buffers around a point shapefile. The process seems to work: (Vector>Geoprocessing Tools> Buffer(s), I select my input layer, leave the segments at 5, and set the distance, create a new output shapefile in the same folder as the input layer, and set the new layer to appear.

A layer IS created, but it's an ovoid ellipse that is massively too large - when I set it for '500 metres', it came out covering most of Eurasia and Africa! I tested the settings, and to at '0.01 metres', it produced an ellipse measuring approx 1200x1450 metres.

What is causing this, and how do I fix it? I wonder if it's related to the co-ordinate system I'm using, as the project is WGS84-PseudoMercator and the input shapefile is WGS84 (I didn't intentionally make them different).

Any help gratefully received! Adam

marked as duplicate by underdark May 20 '17 at 7:43

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I guess that the projection you used is the problem. As far as I am aware off, thr QGIS (I'm using 2.8.1 - but it should be the same) buffer tool use the default measurement of layers coordinate system, thus degrees, not meters. So 500 meters, is actually being treated as 500 degrees - this can explain your outputs.

What you can do, is either project your data to a metric coordinate system, than buffer it. Or convert the buffer value you wish from meters to degrees. Attached images show a creation of buffer using a point layer with WGS84 as its coordinate system. I wanted a 100 meters buffer, and used this site to get a conversion factor for my current latitude. Than I used the 100 meters-degree value (0.0009 approx) to create the buffer. Buffer Tool Buffer Result

  • Thanks dof1985, that looks like my issue. I was under the impression that WGS84 WAS a metric system, obviously a rookie error there. – Adam G Mar 18 '15 at 11:51
  • Good luck. BTW - conversion of the coordinate system of the layer will provide more accurate results, since the precision that is needed to be kept when applying a manually computed conversion factor is too high – dof1985 Mar 18 '15 at 11:54

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