Using QGIS 3 I'm having difficulty with what seems to be a simple problem: for each US state and Canadian province with a coastline (on Shapefile maps I downloaded), replace the coastline segments with a minimum number of segments that will encompass any belonging islands.
Essentially, I want to delete all the coastline vertices except one on each end of the coastline, then extend the coastline by drawing a few line segments out into the ocean (or lake) that will surround the belonging islands, and delete the island vertices from the feature.
I have found very laborious and error-prone ways to do it, but nothing efficient. Ideally, I'd like to select two points on a coastline and delete all the points in between with a command. Selecting the in-between points is clumsy the way I do it, using the vertex tool, trying to "box" parts of the coastline and delete in pieces, zooming in and out, etc. Is there a simple way to do this?
Once I have replaced the coastline with a single line segment, I'd like to stretch it out around the islands as a couple of additional segments. I visualize this as dropping a couple of points into the coastline segment, then dragging those points outward. Alaska has a bundle of islands. It would be great to extend the coastline around the islands, then with some command deletes all the separate polygons (islands ) contained inside the big polygon. In any case, there are probably a number of ways to get the end result.