Tadasuke goes around to different villages and towns to map out the surrounding areas. Since he is not a fighter, he is unable to map out the areas without the player's protection so he may take his measurements in peace. He has not told the player what he is using this surveying data for, but it can just simply be for better maps of the areas.
Tadasuke is a type of NPC that doesn't stay in a single location and can't be found before or after his quests are completed. He appears in the different villages after the danger has passed in the storyline to present a quest for surveying the area. Once the quest is completed, he leaves shortly afterward.