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I am really new to QGIS and I've imported this shapefile of UK with weird lines (the ones not denoted with the red crosses).

What is the fastest way to remove these lines so that it leaves me with just the boundary of UK?

enter image description here

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    I would start with a dataset that had proper topology. Working with this mess is going to be a huge snarl of pain. – Vince May 26 '19 at 22:06
  • @Vince I imported the shapefile from a spatial polygon that I created in R. The problem I am facing is that UK boundary files that are available online are too huge -- it crashes my rstudio. Only this shapefile is small enough to run. Is there a way to get the general boundaries for UK? one with a low level of detail -- i dont need the nooks and crannies, just smooth curves like the one above would do. – imguessing May 26 '19 at 22:15
  • Take a look at natural earth. This may fit your needs. – MrXsquared May 26 '19 at 22:25
  • You have here a non-simple geometry, which can be a pain. A method that works and isn't to time consuming is to convert your polygon to lines gis.stackexchange.com/questions/15819/… , delete the lines that aren't the general boundary of the UK and then convert lines to polygons gis.stackexchange.com/questions/207463/… that said though this geometry is dodgy which makes me wonder what else is wrong here... – Michael Stimson May 27 '19 at 0:09
  • most likely your individual lines (segments) are not ordered, when you arrange them you will be able to build a regular polygon out of them ... – Cyril May 30 '19 at 13:48
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From the looks of it you connected points to polygon, maybe points to lines and then lines to polygon. Problem is that there should be several polygons: Ireland, England / Scotland and one for each of the islands.. Those wierd lines happened because seperate polygon islands were not defined when points were connected so polygon boundary just jumps to next island.

Instead fixing this mess Its probably easier to get proper data which can be obtained from UK Data Service . More on UK boundary is already discussed here..

If shape is too huge you can still use simplify found in processing toolbox of Qgis 3 to reduce number of vertices.

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