arcgis-desktopdeleteeditingfeaturessplitting
I turned editing on and selected this line feature from a feature class. After I selected this line feature, I clicked the Split Tool to separate the line at the vertex (the corner). When I click at the vertex, or any other point on the line, a portion of the line is simply disappearing instead of becoming two separate features. Any ideas on why this is happening?
To update Curlew above, as of QGIS 2.18, you would use the built-in Advanced Digitizing Toolbar, which can be accessed via View > Toolbars > Advanced Digitizing Toolbar. The toolbar will look like this and the "Split Features" button is the fifth from the right:
With that loaded, and the respective later selected and in Edit mode, select the "Split Features" tool and use it to draw through the place(s) where you want to create segments. You can then use the "Node Tool" to select vertices and move them wherever the new segments should be positioned. A quick summary looks like this:
In the end, each segment will then become an independent feature in your vector layer. Be sure to save your edits!
For more information, see the QGIS user manual section on advanced digitizing.
Multi-part lines constructed with tools like Dissolve or Merge do not necessarily order the parts that touch at branches in a sequential order that would keep the parts together. So the line parts on the same physical side of a branch can be on opposite sides of the part sequence internal to the line. Parts are always traversed sequentially by tools. This makes sense for such complex multi-part lines, since once it reaches an end point of a part that touches no other line how can it know which line part to put next? It has no idea what branches may split and which won't, of if one part will have to split into two or more parts when points occur inside a line part, so there is no way to do that organization in advance. Anyway, the polyline parts are never organized in advance by "sides" of an infinite set of unknowable points that could split the line up, and the tool makes no attempt to do tracings while the splits are occurring. Therefore all branches break apart with this tool.
To get branches organized into parts you would need to write your own tool. The easiest process I can think of is to do the splits as usual, that way you will be working with the full set of lines, including new segments that split at places other than the branches. Then buffer the split points by a small distance (say a centimeter or one-half foot). Next calculate the ObjectID of the original lines after the split into a new long field and then make a copy of the split lines. Erase the portions of all copied split lines that fall inside of the split point buffers. Now buffer the copied and trimmed lines by an even smaller distance (say 1/2 centimeter or 1/4 foot). Dissolve the line buffers into single part polygons. Next spatial join the trimmed lines to the single-part dissolved buffers keeping the line shapes. This will associate the buffer ObjectID to the line set that falls within it and they will not cross the split points. Now you can select each line set by that buffer FID, relate them back to the original lines that were not trimmed and Merge/Dissolve each set of lines. Python could do the iterations more elegantly than ModelBuilder, so learn Python.
The rule of geoprocessing is always make complex items the last things you work with. Always work with the simplest items (single line parts) first and then add complexity at each stage of your script in an order that each stage is handled efficiently. Also each additional level of complexity should only be introduced into the process when the simpler objects cannot help move the process forward to the ultimate goal.
Best Answer
I was editing a layer, the layer was a reference of another feature class. So to answer. It wasn't deleting; I don't understand why the line segment was disappearing, but because the edits I was making to the layer were being made to the real feature class (line), I suppose this had something to do with it.
Moral: DO NOT make edits to a layer you created from some selected features. EITHER edit the original feature class objects OR export the layer you created from selected features BEFORE you attempt to make any edits.