This is the part of the project where, having acquired my datasets, I have been cleaning them and converting them into a format I can use in my GIS. This has been more longwinded than it sounds, and what follows is a bit fiddly, but it’s a crucial part of the process. Don’t forget to click on the images to see bigger versions. The main datasets I have been wrestling with recently have been the Historic Environment Record database (kindly supplied by the National Park Authority), the National Mapping Pilot Project data (kindly supplied by English Heritage), lidar data (available from the Environment Agency) and aerial photographs (at the moment, I’m using a combination of prints from the HER and a layer available from ESRI that is similar to google maps). Historic Environment Record There are over 80 HERs in England, each of which contain details and records of the known archaeological sites, finds, interventions and surveys that have been recorded/have taken place within their area of jurisdiction – in this case, the Yorkshire Dales National Park. This makes them one of the major go-to sources for archaeological research. The Yorkshire Dales HER contains nearly 32,000 entries, the majority of which contain details including location and interpretation, and can be searched by various categories. But while the database is a mine of information, there are the inevitable limitations: for example, it has been compiled by numerous people over the years, resulting in a plethora of conventions and standards.
Fig. 1 Each of the red dots on this map of the Yorkshire Dales represents one of the 32,000 records from the HER.
Obviously the records pertaining directly to the individual field systems are of interest, but so is the rest of the database – it provides a useful context against which to examine the field systems, acting as a background view of the prehistoric landscape. Fig. 1 shows the ‘raw’ data with each separate record represented by a dot. The distribution is interesting: the majority of known archaeological sites and findspots cluster in the valleys, with more white space visible on the higher ground – is this a real distribution of past human activity, or a reflection of present activity happening away from the less hospitable peat covered moorland where archaeology-spotting is more challenging?
Fig. 2 Prehistoric features and finds from the HER.
So the first step was to sort the individual records into broad chronological phases, based on the ‘from’ and ‘to’ fields that have been filled according to the interpretation of the inputter. These can be selected from a ‘thesaurus’ of terms, such as ‘Late Iron Age’, so there is a reasonable degree of uniformity, but there is also a spectacular number of different combinations, making life difficult for me. I went for the low-tech approach and, with the help of the ‘find’ function in Excel, removed records for all those sites of unknown date and later-than-prehistoric origin. And then the remainder were broadly categorized into Early Prehistoric, Late Prehistoric and Prehistoric as it was felt that the majority of the features could not be accurately dated more narrowly than this. Their distribution is shown in fig. 2 below. National Mapping Project The NMP dataset is a body of data that dates from the 1990s. It was collected as part of a project conducted by the Royal Commission on Historic Monuments of England with the aim of identifying visible archaeology from aerial photos: the Yorkshire Dales served as a pilot project to assess the effectiveness of the method over uplands. Aerial photographs from the Dales were transcribed, and recognizable features recorded with the use of a system of symbols. As it was done with pen and paper it has since been scanned to produce a digital copy.
Fig. 3 A tile of data from the National Mapping Project. The dotted areas with arrows represent ridge and furrow, the solid lines mark lynchets. The crosses are grid reference points.
When faced with a national park-worth of this data (fig. 3 shows how it arrived), it is quite overwhelming and difficult to work out what’s going on. It arrived as a set of raster files, so the first step was to vectorize it to make it possible to select each symbol individually. This also allows the removal of any smudges, grid reference points or paper ‘edges’ that are not real features. Then it was just a case of assigning each polygon to an appropriate layer category using AutoCAD. When I say ‘just…’, it was actually very fiddly and time consuming, but as a result I have a series of useful, colour-coded layers to add to the GIS (fig. 4).
Fig. 4 An area of NMP data near Kettlewell. The dark green polygons are features interpreted as field boundaries and lynchets; light green represents ridge and furrow; brown dotted lines are tracks; brown represents buildings.
It is not possible to assign dates to the features in the NMP data but it was possible to assign them to broad categories that cover, for example, evidence of extraction industries, ridge and furrow, settlement, and lynchets and field boundaries. Of course, some of those field boundaries belong to prehistoric field systems; the aerial perspective makes them relatively easy to identify (much more so than on the ground). The NMP report (Horne & McLeod 1995) identifies at least 35 prehistoric coaxial field systems. These are shown in fig. 5, alongside those known from the HER data (with varying degrees of confidence), and it is clear that there are already some overlaps and underlaps between the datasets. The NMP dataset in particular gives good coverage of the landscape as a whole, and will, for example, help to explain ‘gaps’ between recorded field systems where more recent ridge and furrow or lead mining is present.
Fig. 5 Comparison of field systems as identified in the HER and NMP datasets.
One of the main reasons for going through these datasets so thoroughly by hand is that I am now much more familiar with the data. I have moved on to processing the lidar data that exists for the Park – more about that next time… Horne, P. & McLeod, D. 1995. The Yorkshire Dales Mapping Project. A report for the National Mapping Programme. Air Photography Unit: Royal Commission on Historic Monuments of England.