OK, I've just resized this canvas and need to move the image down so that I can place a building atop the template.
1. Press the up arrow at the bottom.
2. Press Edit...
3. Press Shift (move the image).
4. Press the down arrow one at a time until the preview reaches the bottom. Then press OK.
5. Press the magnify icon and scroll to the bottom, zooming until the pixels are quite large.
6. One more pixel to go, repeat steps 1-5 :/.
Success!