- the recognition ofhierarchical diffusion,
typically through central place sys-
tems, and frequently operating alongside
the distance-bound,contagious diffusion
of the classical model (Hudson, 1969;
Pedersen, 1970); - the incorporation of rejection and re-
moval processes and the modelling of
competitive diffusions (Webber, 1972).
These changes entailed a move away from
simulation techniques towards more analytical
methods, which have been of immense
importance in the increased traffic between
epidemiologyandmedical geography(see
disease, modelling of). This is now the
major focus of diffusion theory in human
geography, although spatial models of infor-
mation circulation and innovation diffusion
are important in marketing research too.
Haggett (1992) claimed to see parallels
between Sauer’s original prospectus and the
contemporary modelling of disease, particularly
his use of ‘controlled speculation’ and his focus
on ‘hearths and pathways’. Ironically, however,
it was precisely these features that caused
diffusion theory to fall from grace in most other
areas ofhuman geography. There were sev-
eral brilliant studies that wired diffusion into
larger social transformations (e.g. Pred, 1973;
Blaikie, 1975), but these were the exception to
a cascade of studies using available data sets
merely to ‘fit’ or ‘test’ diffusion models. Just ten
years after the translation of Ha ́gerstrand’s
magnum opus, Blaikie (1978) could speak of a
‘crisis’ in diffusion research, which he said
arose from its preoccupation with spatial form
and space–time sequence, while Gregory
(1985) attributed the ‘stasis’ of diffusion theory
to a pervasive unwillingness to engage with
social theoryand social history to explore
theconditionsand theconsequencesof diffusion
processes. Critics argued that the spatial cir-
culation of information remained the strate-
gic element in most applications of the
Ha ̈gerstrand model and its derivatives, and
while flows of information through different
propagation structures and contactnetworks
were exposed in more detail, the primacy
accorded to the reconstruction of these spatial
pathways obscured a crucial limitation of the
Ha ̈gerstrand model: it operated within what
Blaut (1977) called a ‘granular region’, ‘a sort
of Adam Smithian landscape, totally without
macrostructure’. In particular:
(1) The Ha ̈gerstrand model begins with a
pool of ‘potential adopters’ and does
not explain the selective process through
which they are constituted in the first
place. This suggests the need for a
model ofbiased innovation, where (for
example)classorgendercircumscribes
access to innovations. ‘Non-diffusion’ is
then not a passive but an active state
arising directly from the structures of a
particular society (Yapa and Mayfield,
1978). Critiques of this sort required dif-
fusion theory to be integrated with fields
such aspolitical economyandfemi-
nist geographythat pay attention to
the social as well as the spatial.
(2) The Ha ̈gerstrand model assumes a
‘uniform cognitive region’ and does not
explain the selective process through
which information flows are interpreted.
This matters because ‘resistance’ to in-
novation is not invariably a product of
ignorance or insufficient information: it
may signal a political struggle by people
whose evaluation of the information is
strikingly different to that of the ‘poten-
tial adopters’. Critiques of this sort re-
quired diffusion theory to be re-
connected to a more general cultural
geography (Blaut, 1977).These critiques served largely to divert
attention to other projects, however, and there
has been little advance in the architecture of
diffusion theory in recent years. Interest in the
detailed reconstruction of specific diffusion
sequences as key moments in processes of
economic and cultural transformation has
continued in cultural–historical geography
and environmental history (e.g. Jordan,
1993; Overton, 1996), and there is also a
growing interest in the circulation of informa-
tion, including the transmission of scientific
knowledge and the formation of creative econ-
omies (Kong, Gibson, Khoo and Semple,
2006). But these enquiries rarely refer to,
let alone rely on, classical diffusion theory. The
tension between diffusion modelling on the
one side and cultural-historical and politico-
economic studies of diffusion on the other
(and the versions of human geography that
each represents) is exemplified by the study
ofaids. Mapping and modelling the spread
of the disease has been a major focus of geo-
graphical enquiry, but this has been under-
taken largely in isolation from studies of its
social and cultural geography (cf. Brown,
1995). It is in the space between these two
intellectual traditions that diffusion theory
currently languishes, but some small stepsGregory / The Dictionary of Human Geography 9781405132879_4_D Final Proof page 161 1.4.2009 3:15pmDIFFUSION