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I don't understand what Cross does when extracting by location, and how it differs from Overlap- the definition on the user guide is very confusing - it says:

Cross: Returns 1 (true) if the supplied geometries have some, but not all, interior points in common and the actual crossing is of a lower dimension than the highest supplied geometry. For example, a line crossing a polygon will cross as a line (selected). Two lines crossing will cross as a point (selected). Two polygons cross as a polygon (not selected).

Can someone explain this in a clearer way, maybe with a simple example?

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I understand it this way:

Overlap - Tests whether a geometry overlaps another. Returns 1 (true) if the geometries share space, are of the same dimension, but are not completely contained by each other. Only circle 2 is selected.

Share space in this case is meant for polygon. Overlapping polygons share some spce/area so it is used for extracting/selecting polygons.

Cross - Returns 1 (true) if the supplied geometries have some, but not all, interior points in common and the actual crossing is of a lower dimension than the highest supplied geometry. For example, a line crossing a polygon will cross as a line (selected). Two lines crossing will cross as a point (selected). Two polygons cross as a polygon (not selected).

Crossing polygon or two line crossing - this is meant for lines. Cross is used for extracting/selecting lines which crosses any segment of target polygon layer (or line layer), since line with polygon (or other line) can't share any space/area.

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    That makes perfect sense, thank you!
    – Phoebe
    Commented Oct 21, 2019 at 13:53

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