The output of an economic activity, in terms of the economic inputs. Fischer et al. (2007) SSRN, illustrate the ‘central link between productivity and knowledge capital’, and Broersmar and van Dijk (2007) J. Econ. Geog. 8 find that investing in highly dense regions increases congestion, thereby reducing productivity. Some argue that social and environmental ‘costs’ must also be considered; see Compassion in World Farming Trust (1999) on factory farming, for example, and the cost of raw materials is also the depletion of finite resources—see Ehui et al. (1990) J. Env. Econ. & Manage. 18, 2. A productivity rating is an estimate of an area’s ability to support plant growth; see Yang et al. (2005) Rev. Agric. Econ. 27, 1 on conservation reserve enhancement.