Identifiable features that are expected to be seen on the way to a Target.
Walkers should identify tick features along a section of an intended route before setting off towards the Target.
These are then mentally ticked off as each is passed.
Tick features can be anything - e.g. a stream junction, a section of steep ground, the edge of a wood etc.
If a tick feature does not appear where it is expected, then its likely that the walker is off-route.