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
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".