2-D universe

An inter-incarnational sequence of adventures stretched from the Fourth Doctor's encounter with the Iron Legion to the Eighth Doctor's travels with Destrii, (COMIC: Doctor Who and the Iron Legion, The Tides of Time, The Shape Shifter, A Cold Day in Hell!, Endgame, The Fallen, et al.) sharing a continuous reality with various standalone adventures of early Doctors, (COMIC: A Life of Matter and Death, Ground Zero, et al.) the lives of aliens around them, (COMIC: A Ship Called Sudden Death, The Company of Thieves, et al.) and further adventures continuing into the Ninth Doctor's life and beyond. (COMIC: Art Attack, Thinktwice, The Stockbridge Showdown, et al.)

While the majority of sources indicated this reality to be the same as the Doctor's universe as a whole, (PROSE: Deceit, The Scarlet Empress, Prime Time, AUDIO: No Place Like Home, TV: Time Heist, The Doctor Falls, COMIC: Vortex Butterflies, et al.) some, focused on the Sixth to Eighth Doctors, indicated it to be its own reality separate from other strands of the Doctor's life. (AUDIO: Zagreus, Signs and Wonders, PROSE: Spiral Scratch, The Eighth Doctor Part 2, At Childhood's End)

Relation to other realities
During his multiversal adventure, the Sixth Doctor saw a version of himself who travelled with Frobisher. (PROSE: Spiral Scratch)

When Ace was shown her future, she saw "several universes" of possibilities, including one where she was surrounded by giant fleas. (AUDIO: Signs and Wonders) When exposed to anti-time, the Eighth Doctor of the positive-time universe saw himself "on the planet Oblivion facing a race called the Horde". (AUDIO: Zagreus)

By one account, whilst traveling with the Seventh Doctor, Ace was shown multiple possible futures in her timeline by a Quantum Anvil, which included her death in a Nitro-9 explosion. This incident led her to leave the Doctor. (PROSE: At Childhood's End, COMIC: Ground Zero)

Behind the scenes

 * Early Big Finish Productions stories featuring Frobisher were branded as Side Steps into "a 2-D universe".