Orthogonal Edges are an optional feature which is available if you are in
Edit Mode.
Orthogonal Edges can be switched on or off either from the menu bar (View >> Orthogonal Edges) or
from the tool bar. Orthogonal edges consist entirely of segments which
are either horizontal or vertical.
The Orthogonal Edges feature lets you easily create and update orthogonal edges interactively.
Creating orthogonal edges is possible without using the Orthogonal Edges feature, but it
is usually much more difficult.
The Orthogonal Edges feature changes the Edit Mode to ease working with orthogonal edges.
The differences to the Edit Mode without the Orthogonal Edges feature are described in the
following.
 Creating an Edge

If you create a new edge by a drag gesture starting at a node a new bend is automatically
inserted once you leave a horizontal or vertical line starting at the start node. While
you still press the mouse button you can switch between the two possible positions for the bend
by pressing and releasing the SHIFT key.  Updating an Edge

Without the Orthogonal Edges feature, dragging a segment of an edge creates a new
bend at the position where the drag starts. The adjacent edge segments are not orthogonal
in most cases.
With the Orthogonal Edges feature switched on the same gesture moves
the segment instead of creating a bend. Moving a bend also moves a neighboring bend.
Note: The changed update behavior only applies to orthogonal edges. Editing edges
which are not orthogonal is left unchanged by the Orthogonal Edges feature.  Moving a Node of an Edge

Without the Orthogonal Edges feature, moving the end node of an edge usually
leaves the adjacent segment of the edge as a diagonal.
If the end node of an edge is moved with the Orthogonal Edges feature switched on then
the next bend is also moved such that the edge remains orthogonal.
 Removing a Bend from an Orthogonal Edge

If you just delete the selected bend in the following picture…
… the edge becomes nonorthogonal.
If you want the edge to remain orthogonal move the middle edge segment upwards instead.
 Inserting a Bend into an Orthogonal Edge

If you want to insert a new bend into an orthogonal edge press the SHIFT key and then start
dragging the edge segment which you want to split. Without the SHIFT key moving the first
and the last segment of an edge (or the only segment if there are no bends) is constrained
by the adjacent nodes.