According to the National Pork Producers Council meat chart on this website, "leg of pork" refers to the back end of the hog, from which ham roasts are cut. The foreleg is denoted as "shoulder". That which we cook as pork butt roasts and picnic roasts are two halves of a whole pork shoulder. To me, "Butt Portion Leg of Pork" should mean a roast cut from the hind quarter nearest the pelvis.