Mapping

A player of mine has a question (and I’m curious too…).
Mapping says:
Mapping (G): The character can understand and make maps, even if he cannot read or write. With a proficiency throw of 11+, the character can interpret or draft complicated layouts or map an area by memory. This proficiency can be selected multiple times.
What happens if you take this multiple times?

Duskreign’s Minion here.
+4 Bonus each time it is taken. 11+ to 7+ to 3+
“Gaining Proficiencies”
2nd paragraph
“Unless its description says otherwise, a proficiency may only be selected once. If a proficiency can be selected more than once, then the proficiency throw value required for a success is reduced by 4 each time the proficiency is selected.”

Awesome! Thanks!