  A large distance between true and reconstructed core locations of an
extensive air shower (EAS) may results in great systematic mis-estimation of
EAS parameters. The reconstruction of those EASs whose core locations are
outside the boundary of a surface array (outside EAS (OEAS)) results in a large
distance of the reconstructed core location from the true one, especially when
the true core is far outside the array. Although it may not be mentioned, the
identification of OEASs is a necessary and important step in the reconstruction
procedure of an EAS. In this paper, an existing technique is optimized for the
identification of OEASs. The simultaneous use of this technique and a recently
developed approach for reconstructing the core location of an EAS can
significantly increase the sensitive area of a surface array.
