This page (revision-31) was last changed on 18-Sep-2012 10:40 by Alison Bennett

This page was created on 14-Jun-2012 13:25 by David Wheatley

Only authorized users are allowed to rename pages.

Only authorized users are allowed to delete pages.

Page revision history

Version Date Modified Size Author Changes ... Change note
31 18-Sep-2012 10:40 750 bytes Alison Bennett to previous
30 18-Sep-2012 10:38 847 bytes Alison Bennett to previous | to last
29 18-Sep-2012 10:38 843 bytes Alison Bennett to previous | to last
28 14-Sep-2012 15:53 777 bytes Alison Bennett to previous | to last
27 29-Aug-2012 14:05 121 KB Paul Gilman to previous | to last
26 27-Jun-2012 15:05 121 KB Administrator to previous | to last
25 27-Jun-2012 12:46 121 KB Administrator to previous | to last
24 27-Jun-2012 12:35 121 KB Administrator to previous | to last
23 14-Jun-2012 16:32 121 KB Lynn Dyson-Bruce to previous | to last
22 14-Jun-2012 16:31 121 KB Lynn Dyson-Bruce to previous | to last
21 14-Jun-2012 16:31 121 KB Lynn Dyson-Bruce to previous | to last

Page References

Incoming links Outgoing links
SectionE
SectionE

Version management

Difference between version and

At line 2 added 70 lines
HERs comprise both textual records of historical and archaeological sites (or events), and also a map based record of their locations. Historically, in paper-based HERs, the textual (attribute) record was stored on a card index or record sheet, while the locations (geographic information) were marked on a series of related maps. HERs in England usually hold paper maps showing the location of archaeological sites but while computerised databases have now largely replaced card indexes for handling attribute data, it has not been until relatively recently that Geographic Information Systems (GIS) have begun to replicate and enhance the geographic component of HER data.
!!!E.1 Geographic information in HERs: maps and GIS
!!E.1.1 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.
!!E.1.2 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.
!!E.1.3 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.
!!E.1.4 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.
!!!E.2 GIS and spatial databases
Geographic Information Systems are conventionally defined as systems that capture, store, manipulate and output geographical information. Geographical information may be considered as information that is tied into some specific set of locations on the earth's surface, including those immediately adjacent: the sub-surface, oceans and atmosphere. 'Spatial' is now starting to become a commonly used term or synonym for 'geographical'. The term 'geospatial' is gaining currency and also describes the trend towards convergence of spatial technologies such as Global Positioning Systems (GPS), aerial and remote sensing and context-aware computing.
GIS emerged from three principal roots: the need for data analysis and display tools, the automation of map production, and landscape architecture and environmentally sensitive planning. Although GIS have been available since the 1960s, it is only in recent years that hardware and software have become sufficiently powerful and inexpensive for its use to become widespread.
!!E.2.1 Modelling and documenting spatial data
!Layers (themes)
Spatial databases are structured into thematic layers. This means that the system stores geographic data according to the real-world theme to which it relates. A typical spatial database may have separate layers (themes) to represent:
*Topographic height (for example a digital elevation model)
*Soil type
*Rivers and streams
*Roads
*Archaeological monuments
!Vector and raster data
There are two main types of data used in GIS layers: vector and raster, which differ principally in how the system represents the geographic component of the data in a computer file. In a vector representation, the spatial database contains a geometric description of the theme in question, while in a raster representation regularly spaced samples of something are stored.
Vector data is therefore similar to data in a CAD package. Each element in the layer is represented by some geometric entity such as a point, line, or polygon. The process of creating vector data is similar to drawing, using either a digitising tablet or by drawing objects on the computer screen and can be time consuming and expensive. This has the advantages of providing a compact data-storage format, allowing scalable presentation. Being based on geometric objects, it is straightforward to link these to text-based records. Vector representation permits easy quantification of areas and some analytical methods such as network analysis. Ordnance Survey Landline mapping captured at base scales of 1:1,250, 1:2,500 and 1:10,000 for urban, rural and upland/moorland areas respectively, is an example of vector data (in this case containing many different layers). Increasingly though OS Landline mapping is being replaced by the topography layer of OS MasterMap®.
Raster layers are more similar to digital images, as they are made up of a grid of cells, each of which contains a value at a particular location. Raster data is usually generated automatically by scanning paper originals, or obtained from digital sensors (in cameras, or satellites) and is therefore often rapid and cheap to generate. However the quality of the raster dataset is dependant on both the resolution the image is captured at and on the qualtiy of the locational data fixing the position of the image within the GIS. This is particularly suitable for applications requiring display of fine detail (for example aerial photography or historical mapping) but also facilitates many forms of terrain analysis and simulation modelling. Raster data may be dichotomous (that is, cell values are either 1 or 0, to provide a black and white picture) or continuous, where each cell may be assigned a range of values. Examples of widely-used raster data sources include the OS Siteplan® data (for scales between 1:500 and 1:2,500) and Ordnance Survey 1:10,000 and 1:25,000 scale raster products. Raster data is almost always supplied in pre-defined areal units or 'tiles' based on the OS National Grid.
Typical vector applications include spatially referenced database applications – for example, location maps, sites, monuments, artefacts – mapping applications, managing networks (such as roads and utilities) and terrain analysis using TIN elevation models. Raster themes are often employed to analyse continuously varying layers such as slope, elevation or resistivity and remote-sensed data such as satellite imagery. Analyses that employ raster data typically include neighbourhood analysis and overlay operations (for example reclassifying two separate maps of land use and height to obtain an intersected model of land use at height), simulation modelling, predictive modelling, decision support, cost surface and optimum route analysis and visibility analysis.
Many themes could be represented by either vector or raster data models. Terrain, for example, can be represented either by a vector model, using a network of triangles (referred to as a Triangulated Irregular Network or TIN), or by a raster altitude matrix in which each cell contains the elevation at that location. The choice of representation depends on a range of factors, including the capabilities of the software, availability of source data and the intended uses of the data.
Fortunately, most major GIS now work with both types of information, and can use them effectively together. Many forms of analysis (such as visibility analysis or hydrological modelling) can be undertaken using either raster or vector layers, and the two can also be employed together as, for example, when a satellite image is 'draped' over a vector terrain model, creating a 'digital landscape' which a user can explore (rather like a virtual reality 'fly through' (see Figure 39)). It is also possible to automatically convert data from vector to raster and – with some limitations – from raster to vector when needed.
%%image-caption
[{Image src='fig4.gif' alt='Figure 4: Information management cycle.'}]
''Figure 4: Information management cycle''
/%
This page (revision-31) was last changed on 18-Sep-2012 10:40 by Alison BennettTop