I have a load of transect data (in the form of a line shapefile) covering a very large area (approx. 11,900km2) that has been split into 20m x 20m grid squares on QGIS using:
"Vector -> Research Tools -> Create Grid..."
I would like to know how to calculate (without having to physically count) how many of these grid squares my line shapefile covers.
I can only really do simple things on QGIS and don't really use it extensively, so I'm seeking a step-by-step description.
You can use the Field Calculator to create a new field in your line layer using one expression that counts the intersections.
Open the Attribute table of your line layer. Click in the Field Calculator icon
This will open a new window: here you can use create a new field (numeric, Whole integer, 10 of length) and use the following expression
aggregate(layer:='Grid',
aggregate:='count',
expression:=$id,
filter:=intersects(($geometry), geometry(@parent)))
This will create a new field with the count of how many quadrants of the grid each line is intersecting.
Not completely sure about your request: if you want to know the total of the grid quadrants intersected by the lines you can use the same system with this slightly different expression:
sum(
aggregate(layer:='Grid', aggregate:='count', expression:=$id, filter:=intersects(($geometry), geometry(@parent))))
This is the result of the second expression:
Probably not the best visualisation to show but I hope it is a good example to show you the result.
