Samurai Ragazzi: Sengoku Shounen Seihou Kenbunroku

Nobunaga was just taken out of power and there are signs of civil unrest even in the far reaches of Kyushu. A small precinct of Kyushu is ruled by the Harima family and headed by 15-year-old Harunobu who, despite everyone's hopes, has no interest in war or being a lord. Instead, he spends his time surveying the land to make maps or record plant and animal life. Harunobu's dream is to create an encyclopedia that contains all the information in the world. So when the opportunity to travel the world and eventually end up in Rome appears, Harunobu leaves the land in capable hands and sets sail on a journey that he has dreamed of his entire life.

(Source: MangaHelpers)