Seeing a distance means recognising, several strides from the fence, where your horse is going to leave the ground, early enough to keep the canter you have rather than lunge for a spot at the last second. Some riders call the same skill seeing a stride; one skill, two names. It is not a talent you are born with or without. It is pattern recognition, and pattern recognition is built by repetition with feedback.
Want the reps without the horse? Streyed is a training game that shows you hundreds of approaches an hour in your browser and tells you, on every single one, whether you read it right.
Try it freeA distance is not a thing that exists on the ground waiting to be spotted. It is a relationship between three moving parts: the rhythm of the canter, the ground left to the fence, and the take-off spot that rhythm will produce if nothing changes. When those three agree, the fence arrives out of the stride. When they do not, the horse either chips in deep or stands off long.
That is why the riders with the best eye are obsessed with rhythm rather than with distances. A steady canter turns the question into one your eye can answer, because the answer stops changing. An unsteady canter rewrites the question with every stride, and no eye can read a question that keeps rewriting itself.
At the middle of the top pole, and nothing else, from as far out as the turn. It is much harder to judge a target you are not looking at, so give your eye one fixed point and let the ground line, the wings and the strides stay peripheral. Hunting the take-off spot on the floor is the habit that produces last-second decisions, because the spot only becomes readable when it is nearly too late.
The earlier you recognise the developing distance, the smoother the jump: the canter stays level, nothing has to change in the final strides, and the fence comes up out of the rhythm instead of out of a scramble. That is easier on your horse, who in the last moments before take-off can no longer even see the fence directly and is jumping on trust. Every extra stride of notice is a quiet option you still have.
On a horse: canter poles on related distances, a small fence off a circle met out of the same rhythm again and again, and counting down out loud on the approach. All of it works, and all of it is limited by the same thing: volume. A session might give you thirty approaches, and the riders who "just see it" are mostly the ones who have watched tens of thousands.
The recognition half of the skill does not need a horse at all. Streyed puts a schoolmaster called Napoleon in your browser and trains the eye in layers, from holding a rhythm to calling distances good or off to reading a full course. Start with a free day and see how far out you can call your first one.
For the full breakdown of the skill, the reasons it will not come, and the classic exercises in detail, read how to see a stride when jumping.