Problem using Split tool - results in unrelated sections

[SarahSchwarzer2]

Hi there,

I've got a line feature that was created by merging multiple sections of line. I'm trying to split it back up in different places, and when I do, I get multiple splits and lines that are considered one line but are not connected. The image here shows the location I placed the point in a yellow circle. The highlighted line shows one of the resultant lines, while the pink is the other. [ATTACH=CONFIG]26522[/ATTACH]

Is there something I'm missing? I've tried repairing the geometry just in case. I've also made sure nothing else is selected, turned off other layers, anything else I can think of.

Thanks for any assistance!

Sarah

[RichardFairhurst]

Hi there,

I've got a line feature that was created by merging multiple sections of line. I'm trying to split it back up in different places, and when I do, I get multiple splits and lines that are considered one line but are not connected. The image here shows the location I placed the point in a yellow circle. The highlighted line shows one of the resultant lines, while the pink is the other. [ATTACH=CONFIG]26522[/ATTACH]

Is there something I'm missing? I've tried repairing the geometry just in case. I've also made sure nothing else is selected, turned off other layers, anything else I can think of.

Thanks for any assistance!

Sarah

The behavior is normal.  You have dissolved to create a branching multi-part polyline, which will randomly append the order of the internal parts.  Part 1 does not have to chain to part 2, etc.  When you split the break in the internal part order becomes apparent.  You would have to control the part assembly, which is a pain to do unless you wrote a python script.

Anyway, I would do the splits on the original lines or a copy of them and change the dissolve field values at the original lines.  Then use the Buffer tool with a very small buffer and the List option and uncheck the create multi-part option.  Then use Spatial join with the One To Many option to get the polygon Join ID as a new group ID for every set of lines.  Select where the original line attributes equaled the lines and do a new dissolve on the new group ID and the old group ID with the create multi-part feature option checked.  These will create contiguous new branching groups.

[SarahSchwarzer2]

The behavior is normal.  You have dissolved to create a branching multi-part polyline, which will randomly append the order of the internal parts.  Part 1 does not have to chain to part 2, etc.  When you split the break in the internal part order becomes apparent.  You would have to control the part assembly, which is a pain to do unless you wrote a python script.

Anyway, I would do the splits on the original lines or a copy of them and change the dissolve field values at the original lines.  Then use the Buffer tool with a very small buffer and the List option and uncheck the create multi-part option.  Then use Spatial join with the One To Many option to get the polygon Join ID as a new group ID for every set of lines.  Select where the original line attributes equaled the lines and do a new dissolve on the new group ID and the old group ID with the create multi-part feature option checked.  These will create contiguous new branching groups.

Thanks for your reply. I would be amenable to trying to your solution, but unfortunately I'm a little lost. I didn't do a dissolve, and am not sure how to "change the dissolve fields at the original lines." So, missing the first step, I can't continue with the rest. I don't have the original lines, as they were created and merged as I worked. The were not created based on any polygons, and there's no other spatial file that they're related to. I did, however, use the "Explode Multipart Feature" to separate the resultant lines after my split, and then merged the appropriate parts again. I would say the issue is solved.

(Also, I still don't understand why this is the normal behavior for a split, why splitting in one location would cause a seemingly random split in another location, and the line fragments would be considered one line.)

[RichardFairhurst]

Thanks for your reply. I would be amenable to trying to your solution, but unfortunately I'm a little lost. I didn't do a dissolve, and am not sure how to "change the dissolve fields at the original lines." So, missing the first step, I can't continue with the rest. I don't have the original lines, as they were created and merged as I worked. The were not created based on any polygons, and there's no other spatial file that they're related to. I did, however, use the "Explode Multipart Feature" to separate the resultant lines after my split, and then merged the appropriate parts again. I would say the issue is solved.

(Also, I still don't understand why this is the normal behavior for a split, why splitting in one location would cause a seemingly random split in another location, and the line fragments would be considered one line.)

Your solution is fine for a few lines.  I deal with 100K line at a time, so geoprocessing like I mentioned is my only realistic approach.

You need to understand the underlying geometry of a multi-part polyline if you going to work with them efficiently.  Multi-part lines never require that the parts connect to each other.  Gaps are alway allowed within multi-part polylines.  Even if gaps do not appear to occur on a given polyline, splits may create them.

To better understand this, in an edit session select one of your branching polylines and press the Edit Vertices button on the editor toolbar and then press the Sketch Properties button on the Editor toolbar.  The X and Y (and optionally M and Z) coordinates of the line will be shown in the Sketch Properties window.  Each coordinate set is under a header group called Part # beginning with Part 0.  Multi-part lines have 2 or more of these Part group headings.  Click on the first coordinate of Part 0 and then hold the Shift key down while left clicking on the last coordinate in that group.  Right click the highlighted set and press Zoom To.  This is the first part of the line.  Do this for each Part Group.

Now imagine a split in Part 3 of an line that goes up to Part 5.  Every part and coordinate above that split vertice in Part 3 will be assigned to one feature and every Part and vertice below the split vertice will be assigned to another line.  Parts 0-portion of 3 do not have to form a connected chain.  The Parts portion of 3 to Part 5 do not have to connect either.  If Part 3 was the essential connecting line between the parts, splitting of that part will break the line connectivity and form a gap, but it will not affect the ability of any set of line parts to form a single polyline.  Prior to the split they only appeared connected as an entire group, but once broken the part arrangement becomes crucial to determining if the split up multi-line will have complete internal connections or form gaps.

Splitting of a line does not trigger any automatic analysis of the part arrangement to come up with a pattern that would avoid gaps.  Gaps are always allowed and the part arrangement is never altered by the Split tool, whether the result would create gaps or not. 

In a sense the mere fact that there is more than one part to a polyline means that internally there are already gaps or breaks in the line, even if the parts met end to end, which is why gaps are always allowed in a multi-part line.