TRANSIT: a GIS toolbox for estimating the duration of ancient sail-powered navigation

ABSTRACT

Cost-surface analysis in Geographic Information System (GIS) environment has been less frequently used in the study of ancient sail navigation than in other studies of the human past. Navigation cost-surface analysis entails the use of GIS tools that are versatile but not very easy to grasp and to put to work. This article describes an ArcGIS toolbox built to facilitate cost-surface analysis of ancient sail navigation. It estimates the navigation time from a start location, considering parameters relevant for the generation of an accumulated anisotropic cost-surface, automating the complex workflow required to meaningfully pre- and post-process the data. Acknowledging the limitations inherent to the tool, and to the modeling of a complex matter such as sail navigation, the toolbox is first described and then used in a worked example. Historically recorded voyages in the Mediterranean during classical antiquity are compared to estimated durations generated by the toolbox. In spite of structural and expected limitations, the results indicate that the proposed toolbox may produce reasonable estimates. These should be thought of as values gravitating around, not matching, likely past durations. The estimated values may prove useful as an indication of the order of magnitude of past voyages’ duration, and as frame of reference in measuring ancient maritime space through time.

KEYWORDS:

• Classical antiquity
• sail navigation
• cost-surface
• raster analysis
• path distance mapping

Acknowledgments

I wish to thank the Editor, Professor Nicholas Chrisman, for the rapidity and quality of the review process, and the anonymous reviewers for their insightful, helpful, and constructive comments and suggestions that allowed me to significantly improve the article. The help provided by the Editor in amending and polishing my English text is gratefully acknowledged. Thanks are also due to Dr Fernández-López for having made available his very handy rWind package and for the help provided in building an R function to batch download the NOAA wind data; Dr Pascal Warnking for having provided me with a copy of his interesting study on the Mediterranean navigation routes during Roman times. I thank Professor Nicholas C. Vella (Department of Classics and Archaeology, University of Malta) for having introduced me to the intricacies of ancient sail-powered navigation, and Dr Timmy Gambin (of the same institution) for having drawn my attention to the use of GIS in maritime archeology. Needless to say, I am solely responsible for any error or misunderstanding that may linger.

Disclosure statement

No potential conflict of interest was reported by the author.