In a abstract just submitted to Digital Humanities 2011, I labeled Pleiades an "Un-GIS". I feel it's important for users and watchers in the humanities, which is going gang-busters for GIS technology, to understand the differences between Pleiades and a ESRI geodatabase, an OGC-style feature/map service, or a conventional digital gazetteer. I don't think it's useful to try to precisely define "Un-GIS", but here are a few qualities that I think distinguish Pleiades from a typical geographic information system or spatial data infrastructure:
Aggregation of temporally varying features into conceptual places or spaces that reflect ancient practice or modern scholarly method.
Rich toponyms with ancient spellings, transcription details, temporal scope, and links to primary sources and scholarly literature.
Identification and representation of geographic features that have no known locations, or that can be located only vaguely, roughly, or in relationship to each other.
Embrace of the uneven distribution in quality and density of data that is inherent in ancient world studies.
Embrace of web architecture.
Pleiades distinguishes between place and space 1. In writing "Ephesus demonstrates the potential complexity of ancient Mediterranean urban centers" (an example from the DigitalClassicist wiki), a scholar would not be referring to the coordinates of the footprint of Ephesus, but to a historical entity and also the body of work of which it is the subject.
Primacy of space might be the defining characteristic of GIS, but it's the names of places, not their coordinates, that occur in ancient texts and inscriptions. We model toponyms carefully so that we'll be able to serve researchers mining ancient texts for new insights into ancient geography. We're even going to keep track of what the Barrington Atlas calls "false toponyms": place names attested to in ancient or modern works that are now considered to be erroneous. These include names from Avienus' "Ora Maritima" that are regarded to be not just wrong, but fictitious 2.
More common than these false toponyms are names for unlocated places such as Kritalla, the marshalling point of Xerxes' army 3. More common yet are places with fuzzy or non-determinable boundaries like the territory of the Salluvii or the Aegean Sea. Pleiades can identify and represent places for which boundary lines would be misleading. The boundaries of the Roman province of Aegyptus shown on map sheet 100 of the Barrington Atlas, for example, are clearly noted by the editors as rough and approximate 4.
The compilers of GIS datasets (a population that once included me) usually aspire to uniform density and quality of data, and for good reason. The ancient world, however, doesn't give up its secrets like that. Data about it is spotty. Some places are truly lost, some are less accessible. Scholars, too, choose the places that interest them whether they fill in the gaps or not. Pleiades embraces the inherently unfinished nature of ancient studies; instead of waiting on precise coordinates from partners, we're rolling out places with approximate locations that will be refined, live, as we get better locations. I think we're lucky to be doing this now after Wikipedia and OpenStreetMap have completely changed the nature of content and geodata creation – not just in opening it up to non-experts, but in freeing data to be improved incrementally.
Throughout this post, I've provided links to Pleiades using the URIs of places. The representations at the other end themselves carry links to names and locations and neighboring places, and soon (we hope) to digital editions of ancient and modern works served from other domains. We take GIS seriously in Pleiades, but whenever there is a question of "what is the GIS approach" vs "what is the web approach" to a problem, we go with the latter.
Most of all, I offer "Un-GIS" as a starting point for interesting discussions at the conference about how GIS technology and methods do and don't directly apply to historical geography.
Barrington Atlas, Map 15 Arelate-Massalia, compiled by S. Loseby, 1995.
Barrington Atlas, Map 64 Caesarea-Melitene, compiled by T. B. Mitford, 1996.
Barrington Atlas, xxv.