Unexpected result for the Intersection of touching polygons

Question

I have two touching Polygons (two neighbouring counties) and there intersection is a MultiLineString, where:

len(list(counties["King's Co."].intersection(counties["Queen's Co."]).geoms))  
list(counties["King's Co."].intersection(counties["Queen's Co."]).geoms )[0]  
list(counties["King's Co."].intersection(counties["Queen's Co."]).geoms )[1] 

gives:

924
LINESTRING (-7.1060859 53.1680546, -7.1061766 53.1678101)
LINESTRING (-7.1061766 53.1678101, -7.1072205 53.1666679)

I would have expected instead:

len(list(counties["King's Co."].intersection(counties["Queen's Co."]).geoms))
len(list(counties["King's Co."].intersection(counties["Queen's Co."]).geoms)[0])

to give:

1
924

why is intersection giving the result like this? I wish to simplify the borders between a set of bordering counties by reducing the number of points, while at the same time preserving topology.

Answer 1

In your case;

• mls = a.intersection(b) returns MultiLineString.
  
• len(mls)gives you lines' count in mls.
• gs = mls.geomsreturns GeometrySequenceand len(gs) equals len(mls).

So, len(mls) = len(mls.geoms) = len(list(mls)) = len(list(mls.geoms)). More specifically, it's all about __len__() special class method definition.

Note that len(list(mls)) equals len(list(mls.geoms)), however, list(mls)==list(mls.geoms) returns False(but, of course, lines in the lists have similar geometry)