In most cultures the leader of a group or tribe would not be allowed to go first as they are expected to watch their associates and friends suffer horrible fates in the hopes that they will give up valuable information or control of something .
Viggo offered Hiccup a deal where they divide the map in half, Viggo would get the top half and Hiccup the bottom half. At 7.45 Hiccup finds out that Viggo wants to keep him away from a island on his side of the map but when he point to an island that he want to inspect its below the line because the island is facing up with the line above it. The island is on Hiccups side of the map, not Viggo's.