There seems to be some confusion about the Unsplit Line parameter here. The correct descriptions are: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Dissolve/00170000005n000000/ "�?�The Unsplit lines parameter with two options, DISSOLVE_LINES and UNSPLIT_LINES, only applies to line input. When the default DISSOLVE_LINES option is specified, lines are dissolved into a single feature. When UNSPLIT_LINES is specified, only two lines that have a common endpoint (known as pseudonode) are merged into one continuous line."
Thanks for the info. The strange thing is that when I processed the data with the "Unsplilt line" checkbox checked I end up with many lines duplicated. It also seems to dissolve the lines through intersections. Very strange.
Sure, the attached file contains a piece of what I'm trying to dissolve. It contains hydro data which I'm trying to dissolve based on a field called Feat_Code. I used the dissolve tool in the arc toolbox and I'm using Arc 9.3.
I checked the "Unsplit Lines" box and also selected most of the other attributes in the "Statistics Field" option with their appropriate statistic types.
Thank you for providing the test data. ArcGIS 9.3 does have a bug in Dissolve, not doing UNSPLIT correctly. I can't think of an easy workaround. Sorry about the problem you run into.
I have tested in ArcGIS 10 SP3 and Dissolve seems to work correctly; I didn't verify every resulting feature, but a few that didn't work in 9.3. Many features remain unchanged even they have common feature code because they are not connected.
If you can find a colleague who has ArcGIS 10 and can run the process for you, that would be great. Otherwise, I hope you would upgrade to ArcGIS 10 in the near future.
This post clearly explained what I wanted to know. Thanks a lot.
I am wondring if there is any way for the UNSPLIT (or other method) to honor the directions of pre-dissolve lines so that the resulting dissolved line does not flip the directionality of the originals? This turned out critically important since the lines of my road network are digitized along the driving direction. So I would like to maintain the direction of the original lines while reducing the network size by using UNSPLIT.