The Samar Island Natural Park was delineated based on the (a) boundary of the Samar Island Forest Reserve; (b) land classification; (c) existing protected areas within or contiguous to SIFR; and (d) vegetation cover based on 1989 SPOT image interpretation. Adjustment on the SINP boundary was also made based on the ground survey of the actual forest boundary. Alienable and disposable lands along the periphery of SIFR were excluded from the final delineation.

Most of SINP areas are classified as timber or forestlands covered by the SIFR proclamation. However, certain alienable and disposable lands particularly in the vicinity of the municipalities of Concord and Hinabangan in Western Samar were included in the boundary because they are located at core areas and excluding them would be technically impractical.  The boundary of SINP was presented to local stakeholders during community consultations, which have been conducted in compliance to the requirements of the NIPAS Act for PA establishment.

An average distance of two kilometers from the PA boundary was used in delineating the buffer zone. This was based on the assumption that users of forest resources generally prefer to travel up to two kilometers in to the forest in half a day and the other half day going back to their residence so that they could bring their harvest on the same day.  Additional areas covering the municipality of Hernani in Eastern Samar were included in the boundary of SINP to accommodate the request of the LGU to be included in the management of the area.

It should be noted, however, that not all timberlands of the island are covered by SINP.  There are still considerable hectares of forestland outside the boundary of the PA and its buffer zone with sizeable forest cover.