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I have a shapefile (link below) of only watercourses comprised of many short linestrings.

OpenJUMP displays this about each segment

LINESTRING ( 153.05422 -26.44881350000003, 153.05448 -26.448845000000006, 153.05506349999996 -26.448870499999998, 153.06856249999998 -26.448498500000028 )

I wish to join all the separate linestrings segments that have the same NAME and PERENNIALI (Perennial or Non Perenial)

For example: I wish to have all of the Noosa River that is perennial as one selectable piece and another one for Noosa River that is non perennial, and so on for all the watercourses (if there is a gap in the data then I would get a separate line for each piece)

I have used Dissolve from the processing toolbox and this works fine in QGIS but when I save and open another program like JOSM editor the segments are not joined and I do wish to use in JOSM.

I tried 'Vector Geometry>Multipart to singleparts' but cannot work out how to join on the NAME and PERENNIALI attributes.

I notice that the OGR Dissolve only allows one dissolve field option in the Processing Toolbox screen but at the bottom displays the GDAL/OGR console call as ...
ogr2ogr /var/folders/z5/.../OUTPUT.shp "/Volumes/.../Noosa_Hydrolines_named.shp" -dialect sqlite -sql "SELECT ST_Union(geometry) AS geometry, NAME FROM 'Noosa_Hydrolines_named' GROUP BY NAME" -f "ESRI Shapefile"
So, can I alter that to use both the NAME and PERENNIALI and run from the Terminal console?
If so, what changes do I make?

After saving as a shapefile I wish to open in JOSM and select the joined bits a one segment.

I am using MacOS Mojave 10.14.2, QGIS 3.4.1-Madeira (Kyngchaos)

I am a beginner with QGIS or in fact any GIS so simple instructions are preferred.

https://www.dropbox.com/s/y77zrwpsrh9qmmk/Noosa_Hydrolines_named.shp?dl=0

  • 1
    Try running the "merge lines" algorithm AFTER the dissolve. This will cause connected pieces of the dissovled multilines to be combined into a single continuous line string. If this doesn't work, it's likely that there's small gaps between the sections and you'd need to snap them together. – ndawson Jan 29 at 3:12
  • Ok, I'll post as an answer – ndawson Jan 29 at 4:00
1

Try running the "merge lines" algorithm AFTER the dissolve. This will cause connected pieces of the dissovled multilines to be combined into a single continuous line string. If this doesn't work, it's likely that there's small gaps between the sections and you'd need to snap them together first.

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