Neolithic and Bronze Age Landscapes of North Mayo: Report 2011

Creating Digital Archaeological Landscapes: An
archaeological GIS for the NBNM project.
Emmett O’Keeffe, UCD School of Archaeology
Introduction
This report outlines the construction of a GIS for digitally managing and analysing the spatial
component of the NBNM archive. The report introduces the aims and methodology of the GIS
component before outlining the main foci and outcomes of work.
Aims
The general aim of the GIS component of the NBNM project is to digitise the paper archive of four
decades of research on the prehistoric landscapes of North Mayo. This paper archive includes large
and small-scale plans of sub-peat and extant fieldwall survey, plans of excavation cuttings from a
number of excavations of prehistoric sites and detailed mid- and post-ex plans from a number of
excavations. The GIS portion of the NBNM project has focused on the digitisation of the paper
archive; the georectification of all relevant plans; the digitisation of the majority of these plans; the
integration of these with other relevant landscape datasets and the production of outputs.
The paper archive consists of 347 drawings, of these, 288 were scanned as part of Phase 1 with the
remainder being scanned as part of phase 2. These drawings are from a variety of sources such as
original primary drawings, excavation reports and MA theses (Byrne 1986, Dunne 1985). These
drawings vary in source type and consist mainly of: pencil drawings on permatrace, inked drawings
on permatrace, pencil drawings on paper, digitally printed or photocopied drawings. The original size
of these drawings can vary quite considerably from extremely large sheets of permatrace
representing landscape-scale plans of sub-peat fieldwalls to A4 sized plans of numerous excavation
trenches from a variety of archaeological sites.
A methodology was devised to include all relevant drawings within one integrated GIS to allow a series of
analytical and representative options in the future.
The scanning methodology established during phase 1 of the GIS project has been continued. All
image scans are monochrome lineart or greyscale, decisions on the most suitable selection were
made on a case by case basis to produce the clearest images possible from the original paper
archive. A standard scanning resolution of 400 dpi was used and was increased for 80 images when
deemed necessary. All images were saved as .tiff format. Scanned images are organized into folders
by date of scanning and all images follow the nomenclature ‘Scan_###_sitename.tif’, for example,
‘Scan_025_Rathlackan.tif’.
One of the key goals of this project has been the georeferencing of plans of both regional fieldwall
surveys and excavations. Georeferencing an image ties that image into a spatial framework so that it
can be accurately plotted within a framework such as the Irish National Grid. A series of images,
representing the key foci for this project have been georectified. These vary from regional sub-peat
fieldwall plans to plans of individual excavation trenches. This georectification forms the basis for all
digitising work undertaken. Due to the diverse generation methods of the paper archive and the
variation between different projects and different spatial scales a number of methods have been
used to georectify images relating to different geographic foci.
5