"Anchor" is simply a figure of speech - in this case it would the point where the bridge meets land on the right hand side (or perhaps aother vertical tower) showing the bridge is attached to something rather than appearing to be heading off into space.
Neville,
Sky looks better. Image is more realistic.
I think the anchor comment refers to some subject or feature at the edge of the frame to balance, define the image. As it is, the bridge just goes off into the edge of the image and appears cutoff.
Scott
