His ship's logs.
“Funny,” Han said after thinking for a moment, “I have the feeling I’ve been in this area before. Let me check my logs.”
“You keep logs?” Leia was more impressed by the minute. “My, how organized,” she teased.
“Well, sometimes,” he answered as he hunted through the computer readout. “Ah-ha, I knew it! Lando—now this should be interesting.”
“I never heard of that system,” said Leia.
Empire Strikes Back: Official Novelisation
Note that since this doesn't exactly agree with the dialogue from the film, it's considered Legends.
The new junior novelisation simply refers to it as a map.
Han leans forward. “Then we’ve got to find a safe port around here to complete repairs. Any ideas?”
Chewbacca brings up an electronic map on the ship’s main control panel. The small crew pores over it. Han groans. “Anoat system. Nothing around here but mining colonies and…” He pauses. He is suddenly interested. “And Lando.”
The Empire Strikes Back: So You Want To Be A Jedi?
The older junior novelisation concurs. A mapscreen (with a map).
“Then we’ve got to find a safe port somewhere around here.” Han activated a mapscreen on his control panel, and Leia leaned closer to him to study the map. Han asked, “Got any ideas?”
“No. Where are we?”
“The Anoat system.”
The Empire Strikes Back - Official Junior Novelization
This mirrors the note in the junior Storybook. A map of the local systems.
“Then we have to find a safe port around here.” He looked at a map on his computer screen. “Funny. I have the feeling I've been in this area before. Let me check.” He focused an image on the screen. “I knew it. Lando! This should be interesting.”
Empire Strikes Back Storybook