This is the starting picture - the keystone - everything hangs off of it. Look how nothing maintains the horizontal line. Every pic "steps" down.
In this view, I wanted to show how all the pictures "weep" or "slope" down from that center picture.
Martha hangs pictures on horizontal lines, Kate does not. The pictures in this assembly seem - to me - to center around one picture and then "cascade" down on both sides. The genius of this is that when you have dissimilar pictures you never get into a rut trying to make them all match up. If everything is slightly off, slightly off is perfect. Take a look at my markups.
In this picture look at the keystone picture and how there is an X and Y axis to the whole thing. Outside of pic #1, these four pictures anchor the whole assemblage.
To do this sort of thing, you want to start on the floor with all the pics you have available:
• Choose your center pic - it doesn't need to be the biggest, but it does need to have some size.
• The center pic should be precious and needn't attract the most attention on its own.
• Move - generally - from large to small as you move to the perimeter.
• Always allow for more weight or mass on the left (it's just a rule of optics).
• "Weight" means either darkness, size or thickness (this assembly has more pics on the right, but the center pic is moved to the left of your vision so the weight is there)
• When you have your assembly set on the floor, hang from the center pic outward.
• Enjoy. Try it at home.