The central line helps you line up your feet in poses like Warrior, Triangle, Side Plank, and Pyramid
The symmetrical numbers help you
1) place your limbs in the same place on both the right and left portion of poses like Gate, Spinal Twist, and Half Moon
2) place your body in perfect symmetry in poses like Garland, Child's Pose, and Goddess
The symmetrical number system and midpoint help you keep your torso centrally aligned in poses like Seated Forward Fold, Standing Forward Fold, and Half Tortoise
The horizontal lines help you
1) find your shoulder width and place your hands properly in poses like Chaturanga, Forearm Stand, and Crow
2) find your hip width and place your feet and knees properly in poses like Camel, Split, and Lunge
The numbers help you find the right position to place your limbs in poses like Plank, Reverse Tabletop, and Side Plank
Find 4' on your mat between the two 4s, 3' between the two 3s, and so on. Also, each square measures 6" on the vertical side.
The distance between the two outside vertical lines is 14.5". The reason is that the shoulder-width distance for 90% of adult women is exactly 14.5". True story!
However, we suggest that you measure and find your own shoulder-width to be sure. Guys, yours will obviously be wider and kids, yours will be narrower. Check out our blog post on How to (Finally) Find Your Shoulder-width for more info.