The western farthing of the Shire encompassed the land between the Far Downs and the Three-Farthing Stone. Much of the landscape of the Westfarthing consisted of a hilly country of chalk, especially its central White Downs, on which the town of Michel Delving was built. Towards its northern and eastern borders the land became lower, and the valley of the small river known as the Water ran along the northeastern edge of the farthing.
Some of the features on this map were never directly mapped by Tolkien, and so their locations are inferred from descriptions. Specifically, we don't know the exact course of the western border of the Westfarthing, but we do know that the Far Downs marked the Shire's border in that direction. Similarly, the locations of Michel Delving and Longbottom are not established with certainty, but they cannot have differed significantly from the positions shown here.