Description

Archaeological data in a digital mapping environment

The basic types of feature which can be represented in two-dimensional digital data sets are points, lines, and polygons. Archaeological sites might fall into any of these categories. The 'find-spot' of an artefact, such as a coin or a socketed bronze axe, would obviously be a point. Land divisions, such as the Dartmoor reaves, or a structure like Hadrian's Wall, could reasonably be regarded as lines, because although they obviously have width as well as length they are so much longer than they are wide that they would usually have to be shown at scales at which their width would be insignificant. A standing building, or an enclosed area such as a Roman fort or a henge, could be a polygon, because an archaeologist would be interested not only in the boundary of such a feature, but in the interior itself, which you would expect to be different in some way from the 'outside'.

How does the Ordnance Survey treat archaeological sites?

Most archaeological sites are too small to be shown in any great amount of detail in most of the map products available via Digimap, though some appear in outline in the 1:50 000 scale raster data (the Meridian™2 data set, also at 1:50 000, doesn't show antiquities); here are some examples:

 

Fig. 1 Avebury, EDINA Digimap/JISC supplied service © Crown Copyright Ordnance Survey NC/emap/24419

 

Fig. 2 Castlerigg Stone Circle, Cumbria, EDINA Digimap/JISC supplied service © Crown Copyright Ordnance Survey NC/emap/24419

 

Fig. 3 Hardknott Roman fort, Eskdale, Cumbria, EDINA Digimap/JISC supplied service © Crown Copyright Ordnance Survey NC/emap/24419

 

Land-Line.Plus®, however, shows many archaeological sites in considerable detail, depending on their particular characteristics.

 

Fig. 4 Hardknott Roman Fort, EDINA Digimap/JISC supplied service © Crown Copyright Ordnance Survey NC/emap/24419

 

This image is taken from the Digimap website, and shows the level of detail with which the fort at Hardknott is defined in Land-Line.Plus®.

 

Fig. 5 Conwy Castle, EDINA Digimap/JISC supplied service © Crown Copyright Ordnance Survey NC/emap/24419

 

Other remains of buildings are shown in even greater detail, as this Land-Line.Plus® plan of Conwy Castle shows. The standing walls of the defences, the internal buildings, and the external earthworks can all be seen.

 

Fig. 6 Durham Castle, EDINA Digimap/JISC supplied service © Crown Copyright Ordnance Survey NC/emap/24419

 

The Digimap depiction of Durham Castle is slightly different. The outline of the main buildings is red ('building outline'), the symbol used for buildings which are still in use (the Castle is a College of the University); the walls of Conwy Castle are coded as 'general line detail'.

 

Fig. 7 Castlerigg Stone Circle, EDINA Digimap/JISC supplied service © Crown Copyright Ordnance Survey NC/emap/24419

 

Prehistoric sites also feature in Land-Line.Plus®. This is the stone circle at Castlerigg in Cumbria; the stones are represented as point features, so there is no indication of their relative size or their shape, though their positions are accurate.

 

Fig.8 Stonehenge, EDINA Digimap/JISC supplied service © Crown Copyright Ordnance Survey NC/emap/24419

 

The more complex site of Stonehenge has several types of feature. The earthworks are shown as lines coded 'top of slope', displayed in Digimap using a linetype which unfortunately is not available for use in ArcView. Earthworks at other kinds of archaeological site (hillforts, for example) are shown in the same way. The stones themselves are shown in more detail, not just as points.

 

Fig. 9 Stonehenge, EDINA Digimap/JISC supplied service © Crown Copyright Ordnance Survey NC/emap/24419

 

On closer examination, it can be seen that only some of the stones are indicated by lines which show their shape in this more accurate way; the majority are still just points. The difference is between stones which are still upright (points) and those which are lying down (lines) and so have a larger 'footprint' on the ground.

 

Fig. 10 Shap Stone Circle, EDINA Digimap/JISC supplied service © Crown Copyright Ordnance Survey NC/emap/24419

 

This can be seen again in the case of another Cumbrian circle, that at Shap. This is much smaller than Castlerigg, and much less complete, having been damaged by the construction of a railway, but because the stones are recumbent they are shown as lines rather than points.

The appearance of a stone circle in Land-Line.Plus® may not always be a good guide to its prominence in the landscape.

 

Fig. 11 Greta Bridge Roman Fort, EDINA Digimap/JISC supplied service © Crown Copyright Ordnance Survey NC/emap/24419

 

One other point which should be made is that no area features are represented in Land-Line.Plus®, only lines and points. It wouldn't be possible, for instance, to shade in the outlines of the stones at Shap, and areas of vegetation etc. are only indicated as such by the presence within them of point features with the appropriate codes, which can be symbolised using a special font provided by ESRI [opens in a new window].

This section of Land-Line.Plus® shows the corner of the Roman Fort at Greta Bridge in North Yorkshire, with an indication of the presence along the river bank of deciduous trees and scrub. This form of representation gives only a very general idea of the nature of the landscape.

(As described at the Digimap website, area features in Land-Line.Plus® are represented by 'seed points', points which carry a Feature Code describing the area feature type. Area features are used for roofed areas, areas of vegetation and ground cover, cliffs and slopes, and areas of water).

[This description is provided as an indication of the extent to which Ordnance Survey data sets already contain archaeological information. In the GIS exercises which follow the scale of mapping used means that all archaeological sites are treated as point locations.]