Nice.
Below is another map dated 1834 of Vietnam showing the same orientation as you have mentioned, but both maps are of later dates. I am wondering about the cardinal directions used during 2nd Century.
Below is another map dated around 206BC to 9AD, excavated from the tomb site at Changsa, Hunan, China known as King Ma's Mound to which it was believed and recorded by historians and scholars for centuries to be the burial place of King Ma. But through excavation it was discovered to be actually the tomb of Marquis Li Cang. The name of the tomb site, however, remain to this day.
It is hard to make out from the photo, but the map depict the boundary between Changsa Kingdom (Chu-Han or Western Han) and Nam Viet Kingdom. Nam Viet is orientated at the top of the map. Theoretically speaking, if there is a Southern Viet Kingdom, surely there must be a Northern Viet or just Viet Kingdom to start with, since this is a common naming convention for kingdoms. According to the orientation of the map below, it should be located on top of Nam Viet, if so, this is where Vietnam is today. Right?