Question: Scion xA was based on the first-generation vehicle produced since what year?

Context paragraphs:
Toyota Vitz: The Toyota Vitz is a line of three- and five-door hatchback subcompact cars produced since 1999 by the Japanese automobile manufacturer Toyota.  Now in its third generation, the name "Toyota Vitz" has been used consistently in Japan, with most international markets receiving the same vehicle under the Toyota Yaris name, or formerly as the Toyota Echo in some markets for the first generation.  The Toyota Vitz is available in Japan from Toyota's "Netz Store" line of dealerships.

Ford Explorer: The Ford Explorer is a full-size sport utility vehicle produced by the American manufacturer Ford Motor Company since 1990, based since 2010 on a crossover platform.  The Ford Explorer became one of the most popular sport utility vehicles on the road.  The model years 1991 through 2010 were traditional body-on-frame, mid-size SUVs. For the 2011 model year, Ford moved the Explorer to a more modern unibody, full-size crossover SUV platform, the same Volvo-derived platform the Ford Flex and Ford Taurus use although with significantly greater ground clearance.  It is slotted between the traditional body-on-frame, full-size Ford Expedition and the mid-size CUV (Crossover Utility Vehicle) Ford Edge.  Although outwardly similar, the fifth generation Explorer, Ford Edge and Ford Escape do not share platforms.  The fifth generation Explorer does, however, share platforms with the Ford Flex and Lincoln MKT.

AC Propulsion eBox: The eBox is a conversion of a Scion xB hatchback into a battery electric vehicle produced by the U.S. company AC Propulsion.

Toyota ist: The Toyota ist (marketed with a stylized lowercase 'i') is a subcompact car manufactured by the Japanese automaker Toyota.  It is exported to the United States as the Scion xA and Scion xD, the Middle East as the Toyota xA and to Europe and Latin America as the Urban Cruiser for the second generation.

Great Wall Florid: The Great Wall Florid () is a subcompact car produced by the Chinese manufacturer Great Wall Motor between 2009 and 2013.  Styling is suspected to be copied from the first generation Toyota ist (Scion xA), while the nose section is inspired by the second generation Toyota Vitz (Yaris hatchback).

VIU-55 Munja: VIU-55 Munja (Serbian: Муња ; "ightning") is a combat engineering vehicle produced by Serbia.  VTI has done the conceptual design of the "Munja" general-purpose engineer vehicle and the Čačak-based Overhaul Depot has built the vehicle.  The main idea was converting the T-55 tank, using its main structure and subsystems and adding new components, equipment and devices to create a vehicle for entirely different purposes.  Good terrain negotiating ability and ballistic protection of T-55 tank were retained, while engineer equipment and armament were refitted.  It is the first armoured vehicle for the engineer corps outfitted with special purpose engineer equipment and respectable armament, belonging to the most modern designs of this kind.  It is designed to negotiate natural and man-made obstacles, blocking, fortifying and repair of roads and for safe transport of engineer teams and equipment in combat conditions.  VTI designers have thoughtfully arranged accommodation for 8 members of the crew (2 permanent members – driver and deputy commander, also gunner of the 30 mm automatic grenade launcher and 7.62 mm machine gun, and a 6-member troop – commander and section of five pioneers).  Space is also provided for sets of engineer equipment, for mounting of commander’s and gunner’s cupola and associated equipment.

Scion xA: The Scion xA is a five-door subcompact hatchback marketed in the US from 2004-2006 — as an export model of the Japanese Domestic Market Toyota ist.  Based on the first generation Toyota Vitz hatchback, the xA shared a platform with the Toyota Platz sedan.

Maruti XA Alpha: The Maruti XA Alpha is a recently unveilled vehicle produced by Maruti in India.  It was unveilled on 28 May 2012.

Piaggio Ape: The Piaggio Ape (] ; ; Italian for bee), sometimes referred to as Ape Piaggio, Apecar, Ape Car or just Ape, is a three-wheeled light commercial vehicle produced since 1948 by Piaggio.

Scion xD: The Scion xD is a five-door subcompact hatchback marketed in the U.S. and Canada by Japanese manufacturer Toyota beginning with the 2008 model year — replacing the xA.  The Scion xD and the second generation xB were first shown to the public on February 8, 2007 at the Chicago Auto Show.  The xD appeared in Scion showrooms in mid-2007 in the USA and in 2011 for Canada.  The Scion xD was discontinued in 2014, and was succeeded by the Toyota C-HR in 2017.

Supporting paragraphs: Scion xA Toyota Vitz
Answer: 1999