Ardour offers two modes for connecting automation points: Discrete and Linear. To change the mode right click on the automation lane header and choose your mode from the mode menu.

Discrete mode has stair steps between each point on the automation track. This is useful for on-off automation like mute or sustain pedal (on a piano MIDI track).

If you record automation via MIDI (for example a pitch bend from a keyboard), Ardour always uses discreet mode.

Linear mode has straight lines betwen each point on the automation track. This is useful when you want gradual shifts in your automation lanes, such as gradual increase in volume on the fader.