Once a site has been created you can modify it in various ways
Moving Site Nodes
With the Site layer selected in the Nav-Tree, click and drag a site node in any direction to resize the site.
Adding/Removing Site Nodes
With the site layer selected in the Nav-Tree, hold shift (a blue plus sign will appear at the end of your mouse), click to add a node to the boundary of the site.
With the site layer selected in the Nav-Tree, right click on an existing node, and click the remove button to remove the node from the site edge.
Sliding the Site Edge
With the site layer selected in the Nav-Tree, a rectangular grip appears when you hover over the midpoint of the site. Click and drag that grip to resize the entire edge of your site.
