Consider the recreation value that people can
derive from a forest landscape (corresponding
to an entire photo series as described above),
indexed by i, iD.A/, (B), (C), (D); which
may be expressed as a function of the
forest landscape attributes x1, x2, x3 and x4
(corresponding to the different photo pictures
in a series) with viDf .x1; x2; x3; x4/. For a
small change in the attribute vector, we
would have a marginal value function: