Petrovo polje (Peter's Field) is a Undervlašić's plateau at an altitude of about 1140 – 1220 m.
On plateau there is the long samenamed village (Peter's Field) with several hamlets, including registered Đurđevina, Nikodinovići (east) and Peter Field (in the narrow sense), once the center of the local community. It stretches from Đurđevina (elevation 1243 m), with the Mala Ilomska (Small Ilomska) (east) to the proximity intersection of paved local roads of this village crossroad to Skender Vakuf, Turbe and Imljani (west). To the north is bounded by a line beginning a steep slope into the valley of Vrbanja river, on the line of the piks 1220 – 1140 m, and on south − Ilomska valley. Ravne nadbojine (Straight nadbojine) is the protruding part of the plateau towards Ilomska, with Nikodinovići.
On the plateau there are a dozen permanent sources of drinking water, including the famous Kaursko vrelo (Kaursko spring) and Bijeljina. To Peter's field is part of the watershed between the basins of the Vrbanja river and Ugar. In Vrbanja flow Čudnić , Kovaćevića potok (stream) and Ćorkovac, and Ilomska (confluence of Ugar) - Mala Ilomska (Small Ilomska) and Devetero vrela (Nine springs).