The Westphalian Lowland, also known as the Westphalian Basin is a flat landscape that mainly lies within the German region of Westphalia, although small areas also fall within North Rhine (in the extreme southwest) and in Lower Saxony (on the northern periphery). Together with the neighbouring Lower Rhine Plain to the west, it represents the second most southerly region of the North German Plain, after the Cologne Bight. It is variously known in German as the Westfälische Bucht (Westphalian Bay), the Münsterländer or Westfälische Tieflands- or Flachlandsbucht (Münsterland or Westphalian Lowland or Plain).
The Westphalian Lowland consists of the individual regions of Münsterland, the Emscherland in the (western) south, and regions even further south that flank the Sauerland around the Hellweg.
The Westphalian Lowland is classified as a major unit group within the natural regions of Germany and is number 54 in the Handbook of the Natural Regional Divisions of Germany (Handbuch der naturräumlichen Gliederung Deutschlands) and region D34 in the BfN system; both using the same boundaries.
From a natural region perspective the Westphalian Lowland major unit group is sub-divided into the following three-figure major units:
The Westphalian Lowland has the character of a basin because it is bounded by ridges of the Lower Saxon Hills from the northeast to east and by the northern part of the Süder Uplands to the south. These hills rise to heights of several hundred metres above the basin floor.
The boundary of this natural region runs, clockwise from the north, as follows: From Rheine southeastwards along the southern edge of the Teutoburg Forest, from southwest of Osnabrück heading southwest of Bielefeld to the point where the Teutoburg Forest meets the Eggegebirge. From here the boundary runs to the Paderborn Plateau in front of the Egge heading south-southwest via Paderborn and Büren.