A pair of distinguished generators of the fundamental group $\pi\_1(\partial(S^3 \setminus K))$ of the boundary torus of a knot complement are usually called the "meridian" and "longitude". However, this terminology has always seemed a bit odd to me: in geography a meridian is a line of longitude, so shouldn't the curve it intersects be a "latitude"? Does anyone know the origin of this language?



Why is the thing dual to a "meridian" called a "longitude"?
There is a fundamental asymmetry between latitude and longitude on a sphere, whereas on a torus, there is a symmetry between the two generators. This symmetry could motivate the use of nearly synonymous words.


The terminology may originate with the paper [On the homology invariants of knots](https://www.maths.ed.ac.uk/~v1ranick/papers/seifert2.pdf) by H. Seifert (*Quart. J. Math. Oxford (2)* **1** (1950), 23–32). The torus $T$ of interest to Seifert is the boundary of a closed tubular neighborhood $V$ of a knot in $\mathbb{R}^3$. Seifert says that a Jordan curve on $T$ that bounds on $V$ (respectively, on $\mathbb{R}^3 - V + T$) but not on $T$ is called a *meridian* (respectively, a *longitudinal circuit*). Seifert phrases these definitions in a way that highlights the symmetry, which makes the use of near synonyms seem natural.


