The Mapper is an optional item in Going Commando which reveals hidden locations and items on the map, including platinum bolts, desert crystals on Tabora and moonstones on Grelbin.
The Mapper is obtained by visiting the Damosel moon, accessed on Damosel when transforming to Giant Clank. It is won after destroying the Mothership in the mission "Defeat the mothership".
The Mapper functions similarly to the Map-o-Matic in Ratchet & Clank, Up Your Arsenal and Size Matters, and to the Treasure Mapper in Tools of Destruction, A Crack in Time and Into the Nexus. The Megacorp Advisory in Ratchet's commando handbook even referenced the Gadgetron Map-o-Matic, speculating that another similar device could be obtained.