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I would like to select areas under a particular circular radius in QGIS. I believe this is accomplished with the buffer tool, but when I specify the radius the area is not circular.

How to make them circular?

PolyGeo
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Robertg
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1 Answers1

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If you buffer a point, the result will be a circle only as long as you don't re-project the layer.

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I guess you have on-thy-fly re-projection enabled. Try turning it off.

underdark
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  • When I turn off 'on the fly' CRS transformation all of my shapefile layers become invisible. Is this what you were referring to? – Robertg Mar 06 '11 at 18:08
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    They just change their location. Use "zoom to layer extent" to find them again. – underdark Mar 06 '11 at 18:16
  • I'm using google maps as a layer. When I click zoom to layer my points change in respect of their position on the map. – Robertg Mar 06 '11 at 18:20
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    The google maps raster layer cannot be reprojected on the fly. If you want circular buffers on top of your Google map, re-project you point vector layer to "Google Mercator" and re-apply the buffer. – underdark Mar 06 '11 at 18:24
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    I'm not sure how to do that or what it means. Looks like I'm going to have to learn about GIS more thoroughly. – Robertg Mar 06 '11 at 18:31
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    Right-click on the layer you want to buffer, select "Save as ...". Enter target file name and chose Google Mercator coordinate system. Load the new layer and buffer it. Then you should have circles on top of google maps. – underdark Mar 06 '11 at 18:40
  • How can I now use the intersect tool to find areas underneath the buffer? – Robertg Mar 06 '11 at 19:06
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    Just make sure that both layers are in the same coordinate system. – underdark Mar 06 '11 at 19:21