A "Planet Map" is a map commonly used by space travellers in order to see the planets they might visit next. This greatly helps them know which planet comes next, as the Yonder galaxy is pretty big.
Wander once used a planet map in order to see the planets Trudi Traveler had visited prior to the visit at Zizicks.
On the outside, the planet map looks like a normal map. However, once unfolded, it takes an almost identical representation of a specific amount of planets nearby.