Each choice in a check box list questions may have its own field map number. A field map number can be giving to check box choice with the check_box_map function. The check_box_map function takes two string arguments. The first argument is the string value of the choice and the second argument is the field map number.
Creating Custom Check Box Field Maps
check_box_map "red", "2" check_box_map "green", "3" check_box_map "blue", "4"
The check box maps above map the choices with values red, green, and blue to the field maps 2, 3, and 4 respectively.