Buffer around outline of polygon

Question

I'm fairly new to QGIS, and I'm trying to create a buffer around the outline of Spain (including the coastline and boarders). When I do so, it buffers all the country from center to the edge, I just need the edge if that makes sense.

Answer 1

For dissolving polygons for buffer, you can just check Dissolve result option in Buffer parameters:

Answer 2

You need to do the following:

• Dissolve the detailed administrative boundaries based on a field in the attribute table that has same value
• The output of the dissolve will have only one boundary that covers whole Spain.
• Then you can use buffer to buffer the outline.
• If you need only the mainland without considering the islands, then select the mainland and apply buffer on the selected feature.

Answer 3

The trick is to join all the polygons in your map together,

So given (for example) the GB constituencies:

You run dissolve (in the vector geometry menu of the processing toolbox) to give a single (multi)polygon:

Then you can buffer it as you want.