Question: SkyWorld is the fourth public album by a group based on what city?

Context articles: Go-Ahead Singapore
Two Steps from Hell
Classics Volume Two (Two Steps from Hell album)
Halloween (Two Steps from Hell album)
Classics Volume One (Two Steps From Hell album)
Archangel (Two Steps from Hell album)
City of the Fallen
Invincible (Two Steps from Hell album)
Battlecry (Two Steps from Hell album)
SkyWorld

Go-Ahead Singapore is a new Singapore bus operator that commenced operations on 4 September 2016.
 It is a subsidiary of the Go-Ahead Group.
 It is the fourth public transport operator and the second public transport operator operating under the Bus Contracting Model, after Tower Transit Singapore.
Two Steps from Hell is an American production music company based in Los Angeles, California, founded by Thomas J. Bergersen and Nick Phoenix in 2006.
 The company focuses predominantly on movie and trailer music, and has supplied tracks to films such as "Interstellar", "Harry Potter", "Nathan for You", "Pirates of the Caribbean", and "X-Men".
Classics Volume Two, also stylised as Classics, Vol.
 2, is the ninth public album by the group Two Steps From Hell, released in June 2015.
 It features 15 previously unreleased tracks composed by Thomas J. Bergersen alongside 10 new tracks from Nick Phoenix which would later be released in their latest industry album, "Empire".
 The album features tracks containing vocal performances by Felicia Farerre and Aya Peard.
Halloween is the third public album by the group Two Steps from Hell, and was released in September 2012.
 The album contains 48 tracks, written by composers Thomas J. Bergersen and Nick Phoenix.
 All the tracks, apart from "To Die on Halloween", are from their previous promotional releases.
 This public album is the first to have songs with English vocals, including "To Die on Halloween", "This Is Oh My Dear" (a vocal version of "Monkey Business" from the album The Devil Wears Nada), and "Deck the Halls with Blood (from the album Ashes)".
Classics Volume One, also stylised as Classics, Vol.
 1, is the fifth public album by the group Two Steps From Hell, released in June 2013.
 It consists of 23 tracks written by composers Thomas J. Bergersen and Nick Phoenix.
 This album is the first public album available in lossless audio, with others to follow.
 All songs except "Return from Darkness" and "Path to Earth" are from their previous promotional releases.
 The album also features an extended version of "Eternal Sorrow" from the "Nemesis" album, as well as tweaked versions of "Magnan Imus", "White Witch", and "The World Is Mind".
Archangel is the second public album by the group Two Steps from Hell, released in September 2011.
 It consists of 26 tracks written by composers Thomas J. Bergersen and Nick Phoenix.
 The album contains 14 tracks from the album "Nero".
City of the Fallen is a production music company based in Washington DC.
 Founded by Ryan Amon in 2009, the company produces music for movie trailers.
 In early 2012, Ryan released City of the Fallen's first public album called "Divinus", which was made available via Amazon and iTunes.
 In late 2011 after the release of City of the Fallen's 5th volume, "Divine Power", Amon announced that he would be taking a break from writing and composing music for City of the Fallen after focusing on the company for the last 3 years.
 In early 2012 when a fan asked via City of the Fallen's Facebook page if Ryan would resume writing and composing music in 2012, he replied only saying "We think that sounds like a good idea..."
Invincible is the first public album by the group Two Steps From Hell, and was released in May 2010.
 It consists of 22 tracks written by composers Thomas J. Bergersen and Nick Phoenix.
 All the tracks, apart from "Am I Not Human?"
 and "To Glory" (both of which were later released on the album "Nero"), are from their previous releases.
 The album also features modified versions of "Freedom Fighters" and "Undying Love" from the "Legend" album.
Battlecry is the eighth public album by the group Two Steps from Hell, released April 28, 2015.
 It consists of 26 tracks written by composers Thomas J. Bergersen and Nick Phoenix.
 This album features mostly all-new tracks, except for "Amaria" from the "Amaria" album.
 It features vocal performances by Merethe Soltvedt, Nick Phoenix and Felicia Farerre.
SkyWorld is the fourth public album by the group Two Steps from Hell, and was released in October 2012.
 The album contains 22 tracks written by composers Thomas J. Bergersen and Nick Phoenix.
 All tracks, except for "Dark Ages", are brand new original tracks.
 The cover and sleeve are designed by Steven R. Gilmore, with the futuristic city illustration by Sergey Vorontsov.