Here they are the 7 positions for the major scale. At the end you can see the chord assigned to the position. This chord helps you to categorize the box in a particular area on the fretboard for the Ionian Mode. The first box is the number 4, and this is because I always think the Box as to start from the lowest note possible on the guitar. In that case, for Cmaj, it will be F (I am not considering the E open string). Check the Tabs.