Star chart

Star charts were astronomical maps of constellations.

Voyager owned star charts that showed how to access "the dimension of death". Astrolabus had them tattooed onto his body and then ran away. Thinking them stolen, Voyager instructed the Sixth Doctor to reclaim them. He eventually caught up with Astrolabus and Voyager killed him. (DWM: Voyager, Once Upon a Time Lord)