Toroidal grids share a lot with spherical grids (pg. 238 of my book), so some of this may sound very familiar if you’ve been through that. A spherical grid is basically a soup-can wrapper rolled so the east and west edges touch (and then with a bit of magic applied to the north and south edges so they reduce to a point). The same is true of a torus, but with another interesting difference. Picture that soup can wrapper. Now, roll it so that the north and south boundaries touch. Then, taking that cylindrical tube, bend it around donut-style, so that the east and west boundaries touch.