There are two types of bars that represent cables: guyrope and boltrope. Guyrope is what we call external bars (therefore a straight line) which usually stabilizes the structure to the foundations or anchors at perimeter. Every guyrope is considered as a single cable, while a set of boltrope type of bars is considered as border cable (vertex to vertex).
If the mesh has been generated through WinTess3, we can automate the work of generating the cables with the menu Cable | Edit. In some prototypes (conoids, hyperbolic paraboloids, etc.), this work is already done.
For comments on the use of this window see the aforementioned menu Cables | Edit.