This seems to be a map of some kind, however it is very encrypted.
The Queen of Shadows is looking for this map, return to the Thieves' Guild and return it too her.
How to Obtain
Pick the lockbox in the Western part of the Southern Barrens. Two Bandits will attack you when you start to pick it. You must have been asked to go to the Thieves Guild during the Housing quest in order to get the map