L. slab
R. quarter

L. 2 pcs book-matched spiral
R. 1 pc slab

2 piece or 1 piece

Maple backs are available as two piece or one piece (when quality stock permits). The figured grain pattern of maple appears different depending on how the board is cut from the tree. When it is cut parallel to the outside surface of the tree (slab cut) it produces a softer cloud-like appearance. When it is cut 90 degrees to the surface of the tree (quarter cut) the figure appears as straight lines and the pattern will appear bolder looking compared to the same piece cut on the slab.  Angled cuts (spiral/rift) can produce subtle variations between slab and quarter.  

One Piece

As most of the figure in a maple tree is in the often narrower outer layer of light coloured sapwood, and is strongest just under the bark, one piece backs are usually only available as slab or spiral-cut. It is less common to find quarter-cut maple with good figure wide enough for a one piece back, especially for larger instruments. 

Two Piece

As each half of a two piece back only needs to be half the width of a one piece, two piece backs can be cut either on the slab, spiral or quarter. Also, they can be either book-matched (mirror image from a narrower board) or slip-matched from a narrow board folded in half longways.
Apart from the obvious visual difference, any subtle tonal difference between one piece/slab or two piece/quartered can be attributed to the little extra stiffness of quartered wood compared to slab from the same tree.