ACFA’s Survey Approach and Method,
by Fred Hay
The general objective of archaeology is to generate reliable knowledge of the ways of life of past communities. This requires inference from physical evidence obtained not only from under the earth by excavation, but also from the surface of the earth by direct observation in situ, ‘in the field’. The specialist field archaeologist forgoes the recovery of artefacts, evidence of the site’s stratigraphy and of the way in which different contexts of use relate to each other in the vertical profile. Instead, the field archaeologist’s work is limited to observation, recording and reporting surface remains. But the quicker coverage of an extensive area can usefully picture the distribution of human activity in the landscape and indeed identify particular sites worthy of subsequent excavation.
With evidence of this kind, the field archaeologist is constantly faced with problems of dating and interpreting features, as these are usually, but not exclusively, gained through careful examination of artefacts and site stratigraphy, backed up by laboratory-based investigations employing radiocarbon dating, soil analysis and other techniques. But tentative interpretation and rough dating of some features found in the field can be made through comparison with excavated sites, or with unexcavated sites which have been interpreted by a specialist archaeologist. Dating of more recent features can come from local knowledge; from the study of maps; and by documentary research. However, very limited surface evidence of the earliest communities will be accessible to the field archaeologist: the annual cycle of vegetation growth and decay is a soil-creating process, so the accretion of additional soil layers gradually buries early archaeological evidence.
With its dependence on acute observation, two factors can constrain or aid field archaeology: the condition of vegetation and the available sunlight. Most fieldwork is undertaken in early spring with the vegetation at its lowest. Good light is also crucial: the oblique angle of low morning or late afternoon winter sun can often reveal features that would otherwise have been overlooked.
The survey technique normally used by ACFA is the tape-offset method, usually involving teams of three. It measures what is visible on the ground and ‘translates’ these measurements onto board-mounted waterproof tracing-paper, backed by graph paper printed with a 1cm grid, divided further into 10 millimetres. A scale is chosen for the drawing, frequently of 1:100, although scales of 1:1000; 1:200, 1:50 and 1:20 are sometimes employed. At a scale of 1:100, a metre length on the ground would be recorded on the tracing paper as 1cm. The tape-offset method uses two tapes: a longer one forms the straight baseline, normally run out through the middle of the feature or site, overlapping it slightly at each end, fixed firmly to the ground. This is drawn to scale on the board. A second short tape (the offset) is used to take measurements in sequence from points on the baseline – crucially at right angles to it – to selected points on the feature, along both sides of the baseline. The team member tasked with drawing ‘translates’ each pair of measurements (along the baseline and along the offset) into a point on the tracing paper. When all the selected measurements have been recorded, the feature is drawn by ‘joining the dots’, interpolating the intervening unmeasured dimensions of the feature, and adding impressions of other aspects of the site, using conventional symbols (e.g. hachures for slopes). The feature is also carefully located in the landscape (‘georeferenced’). Its orientation is recorded by a compass-bearing taken along the baseline, and a Global Positioning Satellite (GPS) instrument is used to provide a location in terms of the National Grid. So, the feature can be found again on a later visit or by other researchers.
At the end of the survey the completed field drawings are carefully ‘inked up’ on tracing paper, using a fine waterproof-ink pen, and scanned for insertion into the Survey Report, with the feature’s locational data and a verbal description of it, and often a digital image.
