The footprint's fingerprint: on the classification of the footprint family

•A universal footprint definition that is sufficient for all purposes does not exist.•Bibliometric analysis shows the complexity and heterogeneity of the footprint family.•We elaborate on a scheme for classifying the whole footprint family.•It represents a crucial step towards a better understanding of the footprint concept.

Footprints have received considerable popularity throughout the scientific and policy communities, and the sustainability issues concerned have gone far beyond the original scope of the ecological footprint. The footprint discourse, however, has been steeped in controversy. Of particular concern is what actually counts as a footprint. Significant variations of footprint studies in methods, applications and policy relevance make it impossible to come up with a “universal” footprint definition that would be sufficient for all purposes. It is therefore necessary to shift the focus to the classification of the whole footprint family, which is the key to making sense of the footprint concept that is varying across disciplines and evolving over time.

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