N-Space

N-Space (a.ka. Normal Space) was the name given to the prime universe to distinguish it from the smaller E-Space. All but a few of the Doctor's adventures have taken place in N-Space.

Entropy
Because of entropy, N-Space would normally have ceased to exist some time before the 20th century, Humanian Era, if not for the Logopolitans. The Logopolitans used Block Transfer Computations to create the CVEs to vent entropy from N-Space into E-Space. (DW: Logopolis) Sometimes the CVEs also allowed physical objects to travel from N-Space into E-Space. (DW: Full Circle)

Co-ordinates
Unlike E-Space, which uses co-ordinates that have a negative value, relative to navigational system of the Doctor's TARDIS, N-Space uses positive co-ordinates. The Doctor suggested, then, that N-Space was a positive universe and E-Space its negative counterpart.

This was based upon the fact that the TARDIS scanner continued to show images of N-Space even after materialising on Alzarius, which had the same co-ordinates as Gallifrey, though reversed. The Doctor suggested that, rather simplying relaying visual information, the scanner operated off the absolute value of the co-ordinates and thus could not process negative co-ordinates. The scanner system was made functional again simply by replacing its original N-Space image translator with one native to E-Space. (DW: Full Circle)

The Gateway, whose co-ordinates had a zero value (neither positive nor negative) served as a place of transit between N-Space and E-Space. (DW: Warriors' Gate)

Transit points
Aside from the Gateway, objects can pass from N-Space to E-Space via a CVE, as did the Doctor's TARDIS (DW: Full Circle) The Great Vampire traveled to E-Space from N-Space via means unknown, as did the Human ship, the Hydrax (the Doctor surmised that the 'Hydrax' was intentionally brought into E-Space by the Great Vampire) (DW: State of Decay).