  A tight binding model for scanning tunneling microscopy images of a molecule
adsorbed on a metal surface is described. The model is similar in spirit to
that used to analyze conduction along molecular wires connecting two metal
leads and makes it possible to relate these two measurements and the
information that may be gleaned from the corresponding results. In particular,
the dependence of molecular conduction properties along and across a molecular
chain on the chain length, intersite electronic coupling strength and on
thermal and disorder effects are discussed and contrasted. It is noted that
structural or chemical defects that may affect drastically the conduction along
a molecular chain have a relatively modest influence on conduction across the
molecular wire in the transversal direction.
