What is it that makes "The Passionate Shepherd to His Love" by Christopher Marlowe an example of pastoral literature?

A major theme of pastoral literature is that true
happiness can be found in rural areas.  The city is a bad place, but the country is pure
and good.  I think you can see this (at least the part about the country being good) in
this poem.

Look at what the shepherd is offerring.  It is
all pretty much rural stuff.  The only thing that doesn't sound rural is the buckles of
gold for the slippers.

In general, then, the idea seems to
be that the shepherd and his love can be made happy by all this rural stuff.  This
implies that rural life is good and satisfying.