Digital Signal

A "digital" signal (more properly called a "discrete" signal) has only two states: ON and OFF. Presumably, the switch/solenoid will eventually switch states, and then you will have an amplitude that changes over time. The fact that switch and solenoid signals are ON/OFF in nature is what classifies them as "digital" (discrete) signals.

The problem with running discrete signal lines alongside analog signal lines is that the fast rise and fall times of the discrete signals may become coupled to the analog signal lines, the result being brief pulses on the analog signal lines every time the discrete lines change state. It's good that you are using shielded ("screened") cables.

Some analog signals are more susceptible to this kind of interference than others. 4-20 milliamp analog signals will tolerate a lot more electrical "noise" than 1-5 volt analog signals, due to the much lower impedance of a 4-20 mA loop circuit.