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Archaeological Assessment
(developer & land/house-owner)
GIS for Archaeology (IGSS)
In many ways GIS comes into its own when the task is too big to be solved without GIS. (But even if your study is small, please read on).
GIS is, of course, a computer-based technique and the situation for GIS today is not dissimilar to that of computing in the early days (of 1958) when Tom Watson, then IBM chairman, said:
What had computers been used for up until then? Mainly impossibly large tasks like code breaking.
If you want to carry out a countrywide analysis of something that can be mapped (a spatial analysis) then GIS becomes your tool of choice and is really cost-effective. GIS makes distribution maps almost too easy (if you have the coordinate data for what you're plotting).
But GIS really comes into its own when you want to check for concordance between two or more datasets (e.g. artefacts found within 50m of townland boundaries across the Ireland of Ireland). The validity and accuracy of large-scale studies such as this, though, rely heavily on the availability and accuracy of the data. In the example given, can we obtain the outlines of townland boundaries and artefact provenance far better than 50m? Unfortunately, the answer to the second question is no, In many cases only the townland in which the artefact was found is known and in some cases even that is unknown. So the question cannot realistically be asked of the GIS (at least for all artefacts). However, if the question were which monuments can be found within 50m of townland boundaries across the Ireland of Ireland, then the accuracy of the results is assured, providing that a source of townland boundaries is available within budget. The basic study is now really easy and the difficulty is going to be how to deal with the follow up questions. We may notice, for example, that some monument types are more likely to occur near townland boundaries than others - do we need to create more bands e.g. within 20m, 30m, 40m or should we check whether it is proximity to streams, rivers, lakes and seashore (which all often form parts of townland boundaries) that is the common factor. Maybe our study needs to check these in the first phase. Again you need to know that you can access data of the required accuracy within the budget.
For small-scale studies positional data (in two or three dimensions) can be recorded with GPS/GNSS or from measurements taken on the ground from a known datum. (To this end, individual plans can be georeferenced into the big picture). Of course, the smaller the scale, the more accurate measurements need to be and the more costly the GPS surveying equipment needs to be. Topographical scanning with a suitable pole-mounted GPS can reveal archaeological features invisible to the naked eye - a 15cm high bank under long grass for example may become visible on the GIS as linear strings of sample points show increased elevation (and similar slope and aspect at the edges of the bank). Again, the smaller the scale, the more accurate the equipment needs to be and the greater the cost.
As scales increase, desktop topographical surveys can, similarly, reveal larger features using existing elevation (DEM/DTM) data from OSi and others. Again, elevation, aspect and slope can be combined to reveal edges, custom contours can be created or steepest paths can be shown (to reveal ditches or now unused stream-beds travelling downhill for example). At the same sort of scale, aerial photos and even satellite images and data can reveal areas of potential to be investigated further.
Other powerful topographical GIS-based techniques useful in landscape archaeology are viewshed analysis and line-of-sight analysis. A viewshed analysis could show all the terrain that can be seen from a monument - not just from one point, but from any point along a 9km long linear earthwork, for example. A single line of sight may be more appropriate to show that two individual points can be seen from each other though and even if other monuments of landscape features are along the same line of sight.
Many of these techniques are demonstrated in the author's masters' dissertation, which can be viewed or downloaded on this website.
GIS has so much to offer archaeology that it almost defies imagination. Use yours and ask IGSS!
Institute of Archaeologists of Ireland (IAI)
Irish Organisation for Geographical Information (IRLOGI)
Irish Institution of Surveyors
Association for Environmental Archaeology
Royal Society of Antiquaries of Ireland
Archaeology & Development: Guidelines for Good Practice for Developers