Intersect

Similar to the spatial relationships within and contains covered in the previous section, another common geospatial query asks whether two geometries intersect or touch.

Both queries are implemented in shapely:

• intersects(): two objects intersect if the boundary or interior of one object intersect in any way with the boundary or interior of the other object.

• touches(): two objects touch if the objects have at least one point in common, but their interiors do not intersect with any part of the other object.

Let’s try these functions out, for instance, using two lines:

import shapely.geometry

line1 = shapely.geometry.LineString([(0, 0), (1, 1)])
line2 = shapely.geometry.LineString([(1, 1), (0, 2)])

line1.intersects(line2)

True

The lines intersect. Do they also touch?

line1.touches(line2)

True

line1 touches line2. Adding them both to a multi-line is a quick way of drawing them inside a Jupyter notebook:

shapely.geometry.MultiLineString([line1, line2])

We can see here, that the share the point (1, 1), in which line1 ends, and line2 begins. The two lines do not intersect otherwise (‘in their interior’), so the predicament ’touch()’ - as defined above - is true.

If the lines would share some of their interior, that would not be counted as touching. For instance, line1 does not touch line1 (itself), but fulfils all requirements to be counted as intersect()ing with itself:

line1.touches(line1)

False

line1.intersects(line1)

True