Andrew S. Townley wrote:
... I've pulled together some screenshots of a simple example and of part of what I was trying to do as SVG. In doing so, I noticed something that I hadn't noticed before. If you look closely at the lines in both pictures, the "touching" lines are thicker than the external lines. Ideally, I would've liked to have them the same, but in most cases, the image is small enough that you wouldn't notice it. I realize that you end up discussing "inside" vs. "outside" dimensions from a coordinate system point of view, so if you have one 64x64 box starting at (0,0) with a 1px stroke, that stroke should arguably be lines at pixels 0 & 64 in both the x and y directions. If you then positioned the second one at (0, 64), then I wouldn't expect the common line to be twice as wide, but it appears that is the case in the example (http://atownley.org/wip/grid-snap-example.jpg). I've positioned the set on the right as accurately as I could using the x, y, w & h parameters. On the left, this was as close as I could get them to snap with the default settings. ...
It might snap the bounding box of the line instead of the nodes of the line. So try to set on snapping of points and position the nodes using the node editor.
(BTW, in any case, the x, y, w and h values take the stroke of the line into account.)