As you can see from the screen capture below, 2 waterbodies should be merged but were digitized as separate polygons. Using the Select Within Location set to 1m, these waterbodies and others similar, should be the only ones selected but that's not the result I'm getting, all of the waterbodies, no matter how far apart, are selected.
Why is the script not running as I expect it?
Use the following expression to create a unique ID for all polygons that are contiguous or have a distance of max 10 units (change that value on line 6). You could use this to create a new field with Field Calculator.
The expression creates a buffer of 10 meters around all polygons, then dissolves the result to create a multipart geometry, where every contiguous group of polygons is one part. It then checks within which of these dissolved parts the initial polygon is and assigns a unique id for this part.
You could also use the same expression, adding 2 = [expression] with Select by expression to select only contiguous polygons, here the ones with no. 2 (using the data you provided):
The expression to use:
array_max(
with_variable(
'mypolys',
geometries_to_array (
buffer (collect
(buffer (@geometry,10)
),
0
)
),
array_foreach(
generate_series(0, array_length (@mypolys)-1),
case
when within (@geometry, @mypolys[@element])
then @element
end
)
))
