Hardware: Before 1991, AWI data was held by the Nature Conservancy Council on a PR1ME '2255 minicomputer'. At time of transfer in 2001-2002, the database was probably available via networked PCs linked to a server.
Application software: Before 1991 the data was held in a PR1ME Information, PR1ME's database management system. By 1995 the AWI database was part of English Nature's CORDATA information system. The data was held in an Informix UniVerse database with a 'front end' provided by Informix SystemBuilder+. When the AWI was moved from CORDATA to a new information system (ENSIS) in 1995-1996, UniVerse was replaced by Oracle and SystemBuilder+ by Compuware's UNIFACE.
Logical structure and schema: At time of transfer in 2001-2002, the AWI database was held by English Nature in an information system known as ENSIS (English Nature Sites Information System). ENSIS was itself part of a wider system, TENIS (The English Nature Information System). The AWI database was integrated into ENSIS in 1995-1996 as part of the replacement of an earlier information system, CORDATA, of which the AWI database had been a component. CORDATA in turn had replaced a previous system, COREDATA.
The dataset consists of seven tables, four of which are lookup tables linked in 1:many relationships to the main AWISITE table. AWISITE is linked in a 1:many relationship to AWISTRV (ancient woodland revisions), and in a 1:many relationship to AWITNR. Of the lookup tables, SITE was only supplied in part, while NDAD did not receive the CUSTMR table which in ENSIS acted as a lookup table for the CUSTMR_ID field in AWITNR.
How data was originally captured and validated: The AWI was preceded by trials in Norfolk, Lincolnshire and Nottinghamshire. These indicated that it was feasible to identify ancient woodland sites using information from maps and existing survey data, rather than by carrying out field surveys.
The initial stage of the data gathering process involved identifying woods over two hectares on Ordnance Survey First Series 1:25,000 maps, surveyed between 1880 and 1960. These provided a 'base line' for the Inventory, and were used because they excluded afforestation which had occurred since 1945. Other sources used in conjunction with the First Series maps include:
- Earlier 19th century Ordnance Survey maps, including First Edition 1:63,360 maps (surveyed 1805-1873) and 1:10,560 'County Series' maps (largely surveyed by 1900); pre-Ordnance Survey county maps from the 18th and early 19th centuries; and 17th and 18th century estate maps. Likely areas of ancient woodland were identified by their presence on the maps, and as a result of map features which were felt to indicate ancient woodland. These included a wood's name, its situation in the landscape, the nature of the surrounding pattern of enclosure, and the pattern of boundaries in the wood.
- The following were also used as indicators that a site might be ancient: records of ancient boundary features, the presence of a coppice-with-standards or a coppice structure, evidence of former pasture-woodland management, and the presence of species associated with ancient woodland.
- Previous field surveys, published sources, forestry stock maps and information from woodland landowners were used to determine the extent of woodland sites, and whether they were ancient semi-natural woodland or ancient replanted woodland.
- Aerial photographs were examined to determine the current extent of woods, distinguish between ancient semi-natural woodland and ancient replanted woodland, and measure the extent of woodland loss since the First Series maps.
The areas of ancient semi-natural, ancient replanted and ancient cleared woodland were measured on projections of the First Series maps using a romer dot grid overlay. For each woodland considered by the AWI, a data sheet was prepared summarising the information which had been used to determine whether the wood should be included in the Inventory. Data was input to the AWI database for those sites which had been identified as ancient.
Since the publication of the original provisional county inventories, the AWI database has been updated on the basis of more recent surveys conducted by English Nature, local authorities and wildlife trusts, and as a result of comments from the Forestry Commission and woodland owners. Revisions were also made as a result of the project to digitise ancient woodland boundaries, which led to more accurate measurements of the extent of woodland sites. Amendments to the data have included: updating data on a site's conservation status; changes to the site's ownership information; reclassification of a site from ancient semi-natural to ancient replanted woodland (and vice versa); changes to the extent of a site; the deletion of sites or parts of sites previously considered to be ancient; and the addition of sites to the AWI based on new information.
Digital boundary data: By 1994 English Nature had digitised the boundaries of ancient woodland sites in Nottinghamshire and Cumbria, while the Forestry Commission had digitised sites in North Yorkshire. In 1995 a joint project was initiated between English Nature and the Forestry Authority (then part of the Forestry Commission) to digitise the remaining boundaries of ancient woodland in England as part of the Forestry Commission's National Inventory of Woodland and Trees. The digitisation was carried out by the Forestry Authority at 1:25,000 scale using the 1:50,000 maps in the provisional county inventory reports. For some counties 1:25,000 maps were used where available.
The digitisation project is thought to have been completed in 1999. When the first AWI dataset was transferred in 2001-2002, AWI digital boundaries and associated data from the AWI database could be downloaded from English Nature's web site as 26 separate files based on Ordnance Survey grid letters. Each file could be split into up to four sub-files based on 50 km x 50 km Ordnance Survey 'tiles' or quadrants.
Constraints on the reliability of the data: The general limitations of the AWI are discussed in the report by Spencer and Kirby, 'An Inventory of Ancient Woodland for England and Wales' (found in the dataset documentation catalogue). The limitations of the digital boundary data are discussed in English Nature Research Report 313. In particular, it should be noted that the AWI's approach has been to include rather than exclude borderline sites. Sites have been retained in the Inventory even if there is uncertainty over whether they should be classed as ancient, on the grounds that this will allow their status to be re-appraised when more information becomes available.