Pallant Street begins at the Least Gate. Possibly established, in the words of Terry, "by the age-old method, which was to follow the path the cows made down to the river", as it appears to follow the valley between the Tump and Nap Hill.
The Streets of Ankh-Morpork makes the course of Pallant Street clear until it meets an intersection, possibly an open square, where it meets Spa Lane and Hopesprings. On the basis of following the line of least resistance followed by the cows as they found their way to water (and in those days the waters of the Ankh must have been a lot cleaner if cows deigned to drink it), Pallant Street most probably curves round towards the river where it meets Water Street, which crosses Mort Lake to Water Bridge, which opens out into the Fronts and the Unreal Estate on the Morpork side of the river.
The former ambiguity concerning the course of Pallant Street, which presented a headscratcher on The Streets of Ankh-Morpork, is now resolved. The revised The Streets of Ankh-Morpork included with The Compleat Ankh-Morpork now clarifies this issue: Pallant Street does indeed feed into Water Street. The ambiguous alternative direction along formerly un-named streets may now be clearly viewed as a junction with Bake Angels and Brookless End, which feeds directly into Hen & Chickens Field, with Seven Sleepers, Moon Pond Lane and Mystick Alley meeting it from the widdershins side.