Thank you for the interest in NodeXL.
A vertex with no connections to others can be represented as an edge that is a "self-loop" - it originates and terminates in the same vertex. Put the same vertex name in the column for Vertex1 and Vertex2 in the Edges worksheet to create a "self-loop".
It is possible to simply add a vertex (with no edge) to the Vertices worksheet, however, a vertex entered into the vertices worksheet (which has no edge in the Edges worksheet) is by default not shown. To override this setting, change the Vertex Visibility
attribute in the Vertices worksheet to "Show" (rather than "Show if in an edge" which is the default). This can be done directly through the Vertices worksheet by manually changing the contents of the Visibility column. Note that this column
is by default hidden, so you can reveal it via the NodeXL>Show/Hide>Workbook columns menu item.
An alternative approach is to use the Autofill Columns feature in the NodeXL menu. Select the Vertex tab and look for Vertex Visibility. Set this so that it contains "Show".
Vertex Color is similarly set in the Vertices worksheet in the hidden Vertex Color column in the "Visual Properties" group.
If you are also applying "Groups" to the network, you may need to also change the default setting in the NodeXL>Analysis>Groups>Group Options menu item. Here you can control which shape and color attributes are dominant. A vertex can
use the color and shape of its group or use the color and shape assigned specifically to it.