I am currently working on a project to georeference (or georectify) maps of various Egyptian sites from Porter and Moss’ Topographical Bibliography (which can be found online at this Griffith Institute website). Georeferencing is something of a Cinderella job in geographic information systems (GIS) work – its important, but is often ignored in favour of more exciting methods and results. So for those who haven’t had the (sometimes dubious) pleasure of georeferencing a map for themselves, I’m making some videos of the process and uploading them to my own YouTube channel. The first video is available now and features me georeferencing a cemetery at Abu Rawash, north-west of Cairo.
Abu Rawash is the site of the pyramid of Fourth Dynasty Pharaoh Djedefre with cemeteries dating from the Early Dynastic period onwards. Cemetery F, like the pyramid, dates from the Fourth Dynasty and contains the high status mastaba tombs of a number of important royal courtiers. The outlines of these mastabas remain visible in the satellite imagery, with their burial shafts appearing as black marks in the centre of the structure.
Cemetery F was excavated by Bisson de la Rocque, and it is his plan that Porter and Moss include as Map II of volume IIIi of the Topographical Bibliography:
Georeferencing is the process of taking an image and providing it with coordinates that allow the image to be correctly positioned in relation to other geographic data. Most of the historic sketches, excavation and survey plans made by generations of past archaeologists exist as published images. Georeferencing those images is often the first task in collating archaeological data and relating it to modern maps, survey data and satellite imagery.
My task was to use the GIS to locate Porter and Moss’ plan on the satellite image of the mastaba field, allowing, me to obtain geographic coordinates for any of the tombs within it. The georeferencing process I used divided into 3 parts: locating the archaeological features from the Porter and Moss map in the satellite imagery from 2:07 in the Cemetery F video); scaling the Porter and Moss map to the approximately the correct scale (from 2.55 in the Cemetery F video); and then using ground control points (GCP) to link locations on the Porter and Moss map to the same points in the satellite imagery (from 4.30 in the Cemetery F video). This task was complicated by the lack of scale in Porter and Moss’ (1932, Map II) published image (the scale in the image above has been added by me after georeferencing) and the resolution of the satellite imagery, which makes precise location of ground control points difficult at these scales. Nevertheless, the mastabas were relatively obvious in the satellite imagery and georeferencing was therefore easier than it might have been.
The video of me georeferencing mastaba Cemetery F at Abu Rawash, is now available on my YouTube channel and the next image shows the finished project, with the map from Porter and Moss overlaid on the satellite image from the ArcGIS basemap World Imagery layer.
Acknowledgements and References
Porter, B, and Moss, R. 1932, Topographical Bibliography of Ancient Egyptian Hieroglyphics, Texts, Reliefs and Paintings III: Memphis 1. Abu Rawash to Abusir. Oxford.
Maps and images throughout this blog post were created using ArcGIS® software by Esri. ArcGIS® and ArcMap™ are the intellectual property of Esri and are used herein under license. Copyright © Esri. All rights reserved. For more information about Esri® software, please visit http://www.esri.com.
All the satellite imagery used is ArcGIS World Imagery. Sources: Esri, DigitalGlobe, GeoEye, i-cubed, USDA FSA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS User Community.