The Decks visited are the Decks Isaac visited in the first four chapters of Dead Space.

There, he activates the gravity tethers and leaves the Ishimura in an Escape Pod, while getting a transmission from Ellie, who is attacked by a crazed Nolan Stross.

Isaac navigates the Zero-G tram tunnel and proceeds to the Bridge. He finally enters the Tram System on the other side of the Medical Wing, which no longer has gravity. Clarke fights his way through the Medical Deck, his hallucinations of Nicole becoming more and more severe. There, he repairs the Gravity Centrifuge and takes a Tram to the Medical Deck, unable to reach the Bridge due to an unknown obstruction. Isaac then travels through the Flight Deck and then through the Tram Tunnels, encountering several Necromorphs along the way, eventually reaching the Engineering Deck. Having boarded the empty Ishimura through a maintenance entrance built into the hangar, Isaac checks the ship's status on the Flight Deck (from the same terminal he interacted with in the first game). Isaac then must travel into the Ishimura to activate the gravity tethers to reconnect the track. However, Tiedemann uses the Solar Array to fire on the track, severing the rails and almost derailing the trio's transport.

After leaving the CEC Facility tunnel in flames Isaac, Ellie, and Nolan all ride down the rail line on the Transport.

Dead space 2 chapter 2