I'm a recent convert to QGIS but have been confused about the lack of support for drawing curved shapefiles, especially when Arc has almost too many. A lot of the work that our consultancy do is based around natural features such as lakes/rivers so there aren't many straight lines and being able to accurately represent or work with these features requires smooth curves as opposed to the tools I've been able to find on QGIS so far.

Other threads I've found relating to this have stated that being able to draw curves would require a fundamental redesign of QGIS, how is this though?

Other threads also recommend to use a rough shapefile first then simplify/smooth over to produce your curve but i would be worried about using this simply because you can't see the finished lay of the line when you draw it, which could be frustrating if your boundary moves after smoothing.

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    You can use the Spline plugin – gene May 7 '14 at 16:35
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    Would using another free/inexpensive tool in addition to QGIS be an acceptable solution? IMSI (The creators of TurboCAD) for example have a fine free CAD software that is as capable as AutoCAD Lite and an inexpensive full featured solution as well. Your exchange spatial data format between QGIS and CAD would have to be DWG or DXF. – Jakub Sisak GeoGraphics May 7 '14 at 17:06
  • According to this ESRI link, shapefiles do not support curves, only linear approximations. So while a bezier curve tool might simplify the task of creating an input to be linearized, the underlying shapefile will still contain only line segments, not curves. There are other storage representations that do allow curve representations, but the question specifically mentions shapefiles. – Llaves May 7 '14 at 20:42
  • Llaves, interesting thank you for the link it was interesting. Do you have any more details on file types which support curve representations and whether they are supported by qgis/arc? – aheigins May 8 '14 at 12:47
  • QGIS 2.10 has native curve (circulararc) support. In combination with postgis curves can be saved as such. With shapefiles they are segmentized. Unfortunately edit tools are still not available. – Matthias Kuhn Jul 27 '15 at 16:53

As gene mentioned, there is a Spline plugin to digitize curves. Control is limited but it might be a start. Check the plugin settings and adjust the tolerance value to fit your layer CRS and resolution, especially if the CRS is EPSG:4326).

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  • Amazing i just tried it out and it's perfect just what i was looking for! Thanks a lot gene and underdark and thanks for the advice about IMSI jakub but i with this plugin working well i might try avoid doing the CAD dance till later. – aheigins May 7 '14 at 19:20
  • could you just give some details of the use of the tool, because I am unable to even create a new line, not mentioning modifying it. – the world is not flat Jul 27 '15 at 14:50
  • @the_world_is_not_flat Check the plugin settings and adjust the tolerance value to fit your layer CRS and resolution. – underdark Jul 27 '15 at 15:08

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