Currently possible to set two markers in the same position

[mvl22]

If there are two (only two) markers in the same place, the API will complain that the points are too near to each other to plan.

The UI ought to discourage this. Currently in fact it is very easy to do this and not realise - if you click on the Plus symbol (which is an out-of place blue colour, by the way), and not realise that a marker has been set, and you click again, a second marker is set in the same place. The only indication of this is then that the marker's shadow gets progressively heavier.

Though it does make sense if there is more than one point. A manually-planned circular route should be possible, for instance.

I think the rule is that two adjacent points (adjacent in terms of the stack, S,1,2,3,...,F) should not be closer than 100m apart.