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I'm a newbie in GIS and for a project I need to create a shapefile given some points in lat/lon. I have been following this tutorial: https://community.pyramidanalytics.com/t/q5tk8w/creating-a-shapefile-using-latitude-and-longitude-coordinates and it's OK for polygons but I need some lines to be curved.

My data is described given vertices and circles, like this: 3400N 02500W; 3000N 02000W; 3139N 01725W from this point following an arc of a circle 100 NM centred on 3304N 01621W up to 3130N 01545W... and then it continue giving the points of the vertices of the polygon.

(There are other curved parts as well, described like the above part, but I think with one example I'd be able to do the others).

How can I solve this?

  • shape file specification does not support /allow curved line. shapefiles of type line are always connected by straight lines – Kurt Feb 7 at 19:19
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That sounds like parcel or cadastral data. Try one of these plugins (descriptions copied directly from plugin directory):

CoGo Plugin

A plugin to capture coordinates, bearings and distances and to use these to construct and manage land parcels.

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BoundaryDelineation (This plugin is experimental)

Supports interactive delineation of visible (cadastral) boundaries in orthoimages

The plugin is designed to support the interactive delineation of visible (cadastral) boundaries in orthoimages. This work is supported by its4land, which is part of the Horizon 2020 program of the European Union (project number 687828).

Video Tutorial: https://youtu.be/f6an86_-OaY

There are also plugins available for cadastre data for specific regions/languages, including France, Germany, Spain, Slovak and Columbia. Find them by searching for "cadast" in the plugin manager.

As Erik and Kurt pointed out, the shapefile format cannot store a curve. These plugins will help you enter the data, which will be converted to vertices connected by straight lines. If you need it to be stored as curves, look into some of the many other data formats supported by QGIS; there's probably some that can store curves.

These Wikipedia pages may also be interesting:

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Put all points into a shapefile, either by manually entering them in QGIS, or by putting them into a csv and loading it into QGIS.

Buffer the points which are the center of any arc by the given distance (yes, you'll have to convert to km first), then manually draw the polygons using snapping by connecting the points and arcs in the correct order.

Also, note on the side: The common combination of QGIS and shapefile can't do curves. Anything which poses as a curve or circle is just enough points connected by short, straight lines so they seem to form a curve. As @ndawson pointed out, there are some file types which are able to store true curves, and you also are able to manually add curves via the shape digitzing toolbar (https://docs.qgis.org/testing/en/docs/user_manual/working_with_vector/editing_geometry_attributes.html#add-circular-string).

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    Fyi : qgis does have full support for true curved geometries, I've removed your note from the end of the answer. – ndawson Feb 7 at 21:50
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    Don't hurl fragments of information at us, please expand @ndawson. I haven't heard of it. – Erik Feb 8 at 7:54
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    It's been supported since qgis 2.10 - check the changelog – ndawson Feb 8 at 8:02
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    Supported when using PostGIS - that's something different than using plain QGis. – Erik Feb 8 at 8:13

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