This Graph menu command causes independent points to snap to nearby locations when you drag them. Choose this command once to activate it. When snapping is active, a check-mark appears next to the command. Choose the command a second time to deactivate snapping.
The locations to which points snap when this command is active depend on the grid form of the marked coordinate system. For rectangular and square grids, points snap to locations with whole number coordinates (that is, to the integer lattice). For polar grids, points snap to locations whose distance from the origin is a whole number and whose angle with respect to the horizontal axis is a multiple of 15°. In either case, points you drag when Snap Points is active only snap to locations that are relatively close by. In other words, if you have rescaled your coordinate system so that the distance between integer coordinates is great, points you drag will snap only to integer locations that are close to them.