  We characterize transversality, non-transversality properties on the moduli
space of genus 0 stable maps to a rational projective surface. If a target
space is equipped with a real structure, i.e, anti-holomorphic involution, then
the results have real enumerative applications. Firstly, we can define a real
version of Gromov-Witten invariants. Secondly, we can prove the invariance of
Welschinger's invariant in algebraic geometric category.
