From Halopedia, the Halo wiki
Anchor Point would have been set in and around the gas mines of the gas giant Threshold, encountered by the player during the campaign missions The Arbiter and The Oracle and the multiplayer map Colossus. The level would have been set around a camp set up by Sesa 'Refumee's heretic faction. The three support cables hanging from the structure encountered in the campaign served as a skeleton support structure for the level layout, a temporary construction framework resurrected as an outpost by Sesa's troops and cobbled together with nearby debris. The view above the map would have been the gas mine facility itself, while the view below would be the swirling vortex of Threshold's atmosphere.
Anchor Point was developed for Halo 2, cobbled together in about a week. The map only reached one step after the initial block-out, with temporary textures, UV unwraps and lighting but no proper art pass. It was intended as a small map for only four players. This 2v2 map would focus primarily on Banshee dogfighting rather than conventional vehicle and infantry gameplay, though larger scale was tried out. The map was symmetrical, featuring four outer platforms and one multi-level centre area. One iteration of the level had teleporters, though they were removed as they "weren't good". Each of the four platforms would have a single Banshee spawn, and the centre platform would have a beam rifle spawn - the large "tube" connecting the outer and centre platforms was a "not good" experience for infantry players due to the long sightlines and lack of cover, with grenades employed heavily during playtesting. These tube areas were intended to provide cover from Banshees in the sky, though meant experiences running into an enemy player weren't fun.
The map was cut before release as it "played like crap", and the developers at Bungie found the level to not be very fun, as the game's Banshee combat was "messy". Multiple types of gamemode were tested including energy swords-only and snipers-only. However, DeLeon believes the map could have had potential for Capture the Flag gamemodes, if they were able to get round to setting up proper bases. The map was later revealed by artist Vic DeLeon on Twitter on November 10, 2019 for the 15th anniversary of Halo 2.
The map and its files are still playable, with 343 Industries' Jeff Easterling having played on the level fairly recently (as of November 2019). DeLeon also has at least several test maps including a jungle, Old Mombasa and an abandoned Forerunner city.