In QGIS, I am trying to dissolve multiple segments of a river feature and then calculate chainage on the resulting single feature. However, it seems like the internal node/vertex order gets preserved sometimes from the old features, which then causes the chainage plugins (both "QChainage" and "Locate Points Along Line") to calculate the chainage measurements incorrectly along the old segments, rather than understand the new dissolved segment as a single line. Is there a method to correct or reset the internal vertex ordering (I guess that's what it is... I'm not an under-the-hood GIS expert by any means) after the dissolve so this issue won't occur?

Image below displays issue, this is a single line feature resulting from dissolving 2 line segments. The chainage shows it 'beginning' within the line itself near the upper left corner, then jumping back to the other end. This issue occurs when dissolving multiple line features representing a single river in the NHD flowline dataset.

enter image description here

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    Do the two lines actually touch or share a common point? – klewis Aug 22 '17 at 22:28
  • Ki Klewis. Yes, the NHD dataset is designed by USGS to be able to do various network analyses, so the start/end vertices on each segment should be shared/identical. Not to say there wouldn't be errors in a nationwide dataset, but this issue has come up repeatedly for me on the dissolve/chainage workflow. – Bill Hoblitzell Aug 24 '17 at 4:20

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