Removal of duplicate or overlaping spatial objects.

Question

Hi,

I'm trying to reduce a table that has overlapping or duplicate spatial lines and then calculate the length of the remaining lines. However if I have an exact duplicate of 2 lines each with 1 mile length, the spatial summarize and st_length function. would return a length of 2 miles.

However when combining a duplicate polygon the area and length function returns the area length of only the single combined polygon. I.E. a duplicate 1 mile square box would reduce to a single polygon and return an area of 1 sq mile and 4 mile length.

Is this a bug of is there another way to get the output I want?

EdP · Answer

I believe the behavior of the Sum Tool is correct.  It's creating a Poly-line including each line segment.  Think of each of the three duplicate line segments as capturing a person walking between point A and point B.  If you Sum them you get a poly-line that includes the three line segments and the length of the poly-line, correctly, includes the length of all three segments.

Attached is a workflow that

(Option A)  Uses the Unique Tool to either remove the duplicate lines before the Sum Tool.  This doesn't work if the lines have their start/end points reversed.

(Option B)   Removes duplicate points from the poly-line produced by the Sum Tool and rebuilds the line (the effect is to get down to just the two endpoints).

In the real world, I'm hopeful the context of the incoming data can be used to de-dupe before summing spatial data to avoid creating a poly-line based on duplicate line segments.

DuplicateLines.yxmd

Kli_crown · Answer

See the attached workflow. If there's more than one duplicate as mentioned in my other post your workaround fails.

line_weird_2_duplicates.yxmd

Kli_crown · Answer

Your workaround seems indicate what I suspected. The decomposition of the lines includes duplicate points so your work around fails if there is more than 1 duplicate.