2. Close Packing of Spheres - The Square Lattice

In a plane, spheres can be arranged in a plane in such a way that each ball touches exactly four other balls. This is the square lattice.
The plane above and the plane below follow the same pattern.
The spheres from the second plane fit perfectly in the nests form by four spheres from the first plane.
The square pattern is seen better when using struts to connect the nodes.