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B.6 Mapping and spatial data#

B.6.1 Mapping#

The way in which archaeological sites have been mapped varies, but two main types of mapping can be found, with some HERs maintaining both types (Baker 1999a):

• Archaeological constraint areas: this type of mapping attempts to show areas within which archaeological remains are known and/or suspected to survive. This helps archaeologists, planners, developers and others to see rapidly whether a particular development is likely to require an archaeological response. This may also mean that the areas outside the constraint line might be considered to be devoid of archaeological interest and some HERs have, for this reason, decided not to define areas of constraint.
• Archaeological extent: in this type of mapping, the areas indicated are the extents of known archaeological monuments. Where this extent is only approximately known then it is normal practice for a line to be defined around the nearest field boundary. It is usual for linear features such as Roman roads to be delineated and also for find spots to be depicted by a spot or a circle. Where there is uncertainty as to whether the location is correct, a dashed line may be used to indicate this.

The scales used by HERs will vary but the basic mapping is usually 1:10,000 with more complex areas such as historic towns mapped at 1:2,500 or even 1:1,250. Some HERs have mapped directly on to paper or film copies of the OS maps, whereas others use overlays. The advantage of the latter approach is that the overlay is independent of the OS map base, which changes over time.

In practice, most HERs will have a variety of types of maps that have been developed for different purposes and projects. For example, crop-mark sites may be plotted on separate overlays, which can be placed over the main HER maps to enable the user to see the crop-mark features within each HER monument.

B.6.2 Mapping issues#

In HER mapping it is important to consider the following:

• the HER recording manual and user guide should explain how sites have been mapped.
• a consistent approach should be taken to mapping, especially across each type of mapping.
• there should be consistent use of symbols, which should be defined in a key either on the map itself or in the HER recording guidelines or user guide.

Maps form a fundamental tool without which HERs would be unable to function. However, paper maps have their limitations. It can be difficult to keep the map base itself up-to-date. Maps can be time-consuming to use and can be viewed by only a few people at any one time. Only a limited amount of information can be shown on one set of maps or overlays, making it harder to carry out assessment and analysis. For these reasons, most HERs have adopted or are exploring the use of GIS.

B.6.3 GIS and spatial databases#

GIS has much to offer within local government, and is now established as the tool of choice not only for managing spatial information both within archaeological and heritage contexts, but also for all other areas that deal with spatial data including environmental management, planning, rights of way, flood management and many other topics.

As a result, many local authorities have or are establishing corporate GIS-based databases helping to avoid duplication of effort, make best use of resources and bring together datasets which were becoming fragmented. Linking an HER dataset into a corporate GIS means that the HER data can be displayed and related to other datasets held in the authority. These may be topographical, such as contours and rivers, or other planning constraints such as conservation areas and SSSIs. This opens up new possibilities for taking a more integrated approach to planning and conservation.

GIS also opens up avenues for analysis and research into the historic environment. As desktop GIS software develops and its power continues to grow, there is increased potential for analysis and visualisation of datasets, for example in three dimensions or in virtual-reality models. Recent development of web browsers incorporating GIS is enhancing the potential for sharing and display of information through corporate intranets and the internet.

There are now many books on the uses of GIS in archaeology, including edited volumes illustrating the uses of GIS for research and management of projects (see for example Gillings et al 1999, Lock 2000, Westcott and Brandon 2000) and also more general sources (Wheatley and Gillings 2002, Connolly and Lake in press). The ADS's ''GIS Guide to Good Practice'' (Gillings and Wise 1998) provides practical guidance for individuals and organisations involved in the creation, maintenance, use and long-term preservation of GIS-based digital resources and also provides specific advice for HERs.

The aim of this section of the manual is to provide a primer on some of the issues to consider before embarking on system development. It does not set out to review general functionality of GIS in any detail or to review the current GIS market place. Rather, it sets out some of the considerations to be taken into account in establishing a GIS for an HER, and some of the benefits that can be gained through successful implementation.

B.6.4 Having a GIS strategy#

Desktop GIS applications are relatively affordable, and run on commonly available PC platforms. However, the overall systems cost to put together an HER application (including procurement, customisation, data capture, maintenance, mapping) remains high. Although elements of the system-development life cycle may sometimes be missed out, this will generally be a false economy. For example, omitting a clear and well-thought-out statement of user requirements will, at the minimum, make it difficult to measure whether the system has fulfilled its anticipated purposes, and at the worst, result in frustrated users and managers who feel 'let down'. The development of systems that will meet needs over the life of the system and that enable the information held within them to be transferred to future systems requires careful planning. Significant changes after system implementation can be very expensive.

Many local authorities will have either departmental or corporate policies governing GIS. These may include standards for hardware and software, data standards and policies for access. GIS is well suited to a corporate approach to data management, since it can bring together information from different sources, and even different data types into a single, spatial view. For example, GIS allows users to select a location (for example a property address) and to display text information from a database of planning proposals, a listed buildings database, an HER database or other digital information such as a scanned property deed from the record office or photographs from the engineer's department.

As with most computing, the continuing emphasis on communications and IT in higher education ensures that there is a growing awareness of GIS amongst recent graduates. For existing HER staff, training in the corporate GIS is generally available either from the local authority or from commercial training providers. There are also courses offered by university continuing education departments and others on the use of GIS in archaeology and for conservation.