Assessing visibility and geomorphological biases in archaeological field surveys: a case study on an early Roman colonial landscape in Central-Southern Italy

Anita Casarotto, Tesse D. Stek, Ruud van Otterloo, Jan Sevink


There is general agreement amongst landscape archaeologists that survey data can be biased by many factors such as ground visibility conditions and geomorphological processes (erosion and deposition). The visibility conditions of investigated fields may play an important role in favoring or preventing the recognition of archaeological materials during field survey. Moreover, erosive and sedimentary processes that occurred after the primary deposition of these materials, can delete or obscure part of the archaeological record. In due course, these factors are likely to distort the original settlement history in a landscape. Therefore, it is of vital importance that archaeologists check their legacy data obtained by surveys for potential biases, before they use these data to assess ancient settlement patterns and location preferences. This paper presents a GIS quantitative approach for the evaluation of visibility and geomorphological effects in large scale, site-oriented field surveys conducted in the early Roman colonial territory of Aesernia (Central-Southern Italy). By means of a combined application of statistical tests and geo-pedological analysis the extent and scale of these biases are translated into GIS maps indicating the likelihood that negative field survey observations (absence of sites), in specific parts of the landscape, are genuine or rather the result of the aforementioned biases. These ‘archaeological detectability’ maps allow researchers to formally highlight critical surveyed zones where the recording of evidence may be unreliable, and thus provide a filter through which archaeologists can calibrate their interpretations of legacy site distributions.