OpenStack moving node in Network Topology

I am totally new in OpenStack. After launching the Stack, it shows a network topology in a project. There are two different ways to represent the topology. One is shown like the figure 1 enter image description here. Other way is shown like this figure 2 enter image description here.

My question is, why do the nodes in figure 2 always move randomly? Is there some ways to fix the nodes in a particular point, not move randomly?

Thanks for your help

via Otto Gao