1 Of a river, the bed, and banks.

2 A point or limit that distinguishes one social system or group from another and identifies and regulates who may participate in it. Such boundaries may be contested, but Painter, in P. Cloke and R. Johnson (2005) notes that ‘It may be impossible to draw a sharp territorial boundary between “British society” and “French society”, but social processes operate (somewhat) differently in Britain and France and there are real differences between social structures and social institutions in the two countries’.

3 A line around the edge of an area; a perimeter. J. Nevins (2002) suggests that a boundary is a strict line of separation between two (at least theoretically) distinct territories, where a border is an area of interaction and gradual division between two separate political entities.

Mostly in biogeography and plant ecology, boundary detection is the identification of the zones of greatest change in vegetation and associated abiotic/biotic factors; see Jacquez et al. in T. Poiker and N. Chrisman, eds (1998). Kent et al. (2006) PPG 30, 2 are a model of clarity in discussing boundary detection. The extent to which geographically isolated regions support local diversification should predict the placement of biogeographical boundaries (Patten and Smith-Patten (2008) J. Biogeog. 35, 3).