Legacy Astrographic Data
The Legacy Astrographic Data is the chaotic set of sector and subsector data sets that arose during the period of 1977 to present.
History & Background
Traveller astrography is very difficult to document because it has had many overlapping periods about which even the direct eye witnesses and participants sometimes have profound disagreements. The legacy data is the interaction of the official publications, the work of the various Traveller licensees, and the fan works. Because these works fed into each other in various random ways, tracking the exact history of some of the data can be a difficult task. This author can only confess to having reviewed forty years of published materials, spoken with multiple former employees, authors, illustrators, and other participants and tried to piece the best history possible out of the mess. 
Initial Sectors (1977 to 1984)
Rules for generation of astrographic data was included in Worlds and Adventures (1977), and could be used to generate map data (See TAS form 6, in the same book). The generation rules were expanded with the publication of Scouts (1983). There are several variations of system generation through each version of Traveller.
The first official publication of sector data was The Spinward Marches (1979) which has a full sector with maps. Several of the adventure books published by Games Designer Workshop includes excerpts from the The Spinward Marches book. For example The Kinunir (1979) has a full hex map of Regina Subsector.
In 1980, Library Data (A-M) (1980) has the first full map of charted space (pages 23-24), but with no world locations.
In 1981, Judges Guild published four sectors: Ley Sector, Crucis Margin, Maranantha-Alkahest Sector, and Glimmerdrift Reaches which included 22"x34" maps and full data. These sectors have later been overwritten. Also in 1981, Paranoia Press published maps and data on two sectors: Beyond and Vanguard Reaches.
In 1984, Games Designer Workshop produced Atlas of the Imperium incorporating previous data plus computer generated data, producing maps for 35 sectors of the Imperium. These contains system locations, and a few system details. The data behind the AotI has never been published and is presumed lost. Vargr (1984) published map and full data for the Gvurrdon sector.
In 1984, 1985, and 1986, each of the Alien modules (Aslan, K'kree, Vargr, [[Zhodani (Alien Module)|}}, Droyne, Solomani, and Hivers) contained more detailed maps including some sector names, but no additional data.
Source of data was in physically published works. In addition to the many works of Game Designers' Workshop, and the several licensees, there were several fanzines also publishing astrographic data. Access to data required knowledge of the publishers and purchase of the physical media.
Digest Group Publications, a Traveller Licensee, with the publication of The Travellers' Digest (1985) magazine generated several sectors of data. In total they generated 35 sectors of data. They reverse engineered the AotI maps to some success. This data was used in their various of the DGP publications throughout their history. The data was used as the basis for the dot maps in Solomani & Aslan and Vilani & Vargr.
Vilani & Vargr (1990) and Solomani & Aslan (1991) include detailed dot maps, showing the location of star systems across most of the charted space map. Other than the GEnie Sectors, this data was never released. Fans have reverse-engineered this data.
History of the Imperium Working Group
The History of the Imperium Working Group, founded in 1987 with the publication of MegaTraveller, had the explicit goal to document the future history of the Third Imperium. This would include all aspects of the Traveller universe. This data was shared via the physically mailing floppy disks containing various documents.
HIWG divided charted space into four quadrants, and several smaller sections. These sections were claimed by members of HIWG for development and detailing.
During it's history, HIWG members add data for more than 100 sectors. When the GEnie data was published, this was added to the data set. The members also reverse engineered and generated data for most of the sectors published in V&V and S&A.
The GEnie and HIWG expanded data continues to be used widely by Traveller fans for their projects. The Hinterworlds Sector article in Challenge 39 used the data as its starting point. The data for the Gateway Domain sectors was used as the starting point for Gateway to Destiny. It served as the basis for the T5 Second Survey.
The data, as updated by HIWG, is distributed with Galactic and Heaven & Earth, two of the most popular Traveller mapping programs. Different releases of the programs have different version of data depending upon what was available to the developers at the time. It forms the basis for numerous online maps. The different versions of the data eventually ended up on Sunbane and other servers (Missouri Archive, Core, etc.) It also ended up on numerous internet fan sites including the Interactive Atlas of the Imperium, Map of Traveller Charted Space, TravellerMap, and others.
Early Internet Era
From the late 1980's to the early 1990s, access to data during required knowledge of the pre-web internet, including subscribing to the TML or other mailing lists, knowledge of various FTP sites, and being a member of online services like CompuServe or GEnie. Most people still had access to data only via the published works.
From the late 1980s and through the 1990s additional variations on maps and data occurred from the MegaTraveller, Traveller The New Era, and Marc Miller's Traveller settings. The Traveller fan base also continued to generate, refine, and update parts of the data.
From around 2001 to around 2016, there were several additional projects such as Clifford Linehan's Core Route project, generating data and publishing it online. Other projects were generating data for the edges of charted space including the Vargr Extents,
T5 Second Survey
With the publication of the playtest version of the Traveller 5th edition core rule book (2008), Don McKinney, Robert Eaglestone, along with Marc Miller engaged in a project to collect and update the known astrographic data. Since the original three members, others have joined and left this ongoing project. The project was to identify and correct consistency errors between Sunbane and AOTI astrographic data.
The T5 Second Survey mandate originally included the 35 sectors of the Imperium. The project completed in 2012 with publication to the Traveller Map site. From there the project as continued with an expanded mandate to support any of the Traveller publishers to produce a consistent astrographic data set.
Despite the presence of the T5 Second Survey players continue to enjoy the process of generating worlds and sector data as part of the Traveller Universes publishing their efforts on line.