I believe it is the Topographic map.
It's to emphasize the seriousness of his words.
Hope I helped!:D
It can set a point of view, or perhaps a time frame in which the story occurred, this is a very complicated question to answer without reading the book, sry
They would best there meat till they would come then mix it up with a chilly powder
Dark and mysterious
when put in your depth I feel pain slide away
my emotion remains settle wile your waves carry me away
drifting in the night, your cold touch gives me a chill
your smooth sensation does more than just fill
my heart is now steady
and suddenly i'm ready
to drift off in your waves of depth, darkness and mystery
( im not very good but i hope it helps)