1) A way of traversing the track from the mast to the next one, so that that state of all that track can be interrogated:  How turnouts are set, whether it's occupied, etc.

2) The state of the next signal

A similar approach is implemented in AutoDispatcher.  User can define the indication (aspect?) to be used depending on:

1) Setting of turnouts from mast to the next one (whether turnouts, if any, are all closed or not);
2) Indication (aspect) of next mast.

If any block between present and next mast is occupied, aspect is defaulted to "Stop and stay"

User then can match Indications (Aspects?) to Apperances of multi-head masts.