Why do Baked Hams usually have a checkerboard pattern along the top?

Unlike a brittle skin, it's quite easy to cut superficial slices in ham, and many cooks find the pattern visually pleasing. Chances are, that scoring of ham was originally initiated for more practical reasons. Pork experts say this process began with the old-style hams that had more fat. The scoring, or slicing, of the surface was done to allow the fat to drain during cooking. Hams today are much leaner, so the scoring may be done simply for visual reasons. Since the hams are lean, it is important not to score too deep. This will cause the natural juices to run out and make the ham very dry. Occasionally you will buy a ham with a checkerboard pattern already on it. These are imprints of the netting used to hold-shape the meat during curing. Nettings (or "stockings") are used in curing of boneless hams, which tend to bulge if left to cure without "undergarments."
http://en.wikipedia.org/wiki/ham