Selecting polygon features that are not fully contained against neighbors in QGIS?

Question

In QGIS what would be the best method to select features that are not fully contained against it's neighbours?

For example I want to select local authorities that have a coastline so in the example below how would you select the ones highlighted in yellow.

Obviously you could manually select them but this can be time consuming on larger datasets and is prone to error.

Answer 1

If you have a shapefile of the coastline then great, skip to Step 3 otherwise:

1. Use Dissolve your polygon shapefile.
2. Use Polygons to lines on the output of Step 1.

3. Use Select by location and choose the relevant options such as selecting your original polygon layer to select the features from and the output of Step 2 to use as the intersection layer. Use the geometric predicate touches which means it should select all polygons which touch the coastline: