Geographic Entity

By Geographic Entity, we mean any geographic object (physical, cultural or conceptual) that can be identified and discussed by humans.

In an unproblematic modern context, a Geographic Entity can be named and can be located precisely. In historical contexts, we may be unable to determine location, or we may be able to do so only imperfectly. On the other hand, we may be able to locate accurately an entity of interest, but we may be unable to discover its historical name(s), or we may be able to associate an attested name with a located entity only tentatively. Temporally, names come in and out of use. For some entities, their locations and geospatial extents (the footprint or area of a province or lake, for example) can also change over time. Our ability to track these changes accurately varies. For examples of some Geographic Entities as represented in the Barrington Atlas, see: BAtlasEntityExamples.

In terms of our computational context -- the Pleiades system itself -- we have created a Geographic Entity Content Type. These objects are the most general type of record in our data store. Therefore, they constitute a major organizing mechanism for our data, as well as a primary point of interface and interaction for our human users and for various automated applications. Some of our applications and user interfaces will treat entities as cartographic features. Others will treat them as collections of names or other attributes.

Our goal in the ongoing design and refinement of this content type is the ability to support all types of data represented cartographically and textually in the Barrington Atlas and its Map-by-Map Directories.

Key Aspects

Some key aspects of our design deserve highlighting:

An entity may have zero or more Geographic Names

The Barrington Atlas makes this distinction. The maps, of course, are filled with physical features, only some of which are labeled. Culturally significant sites are usually labelled with their attested names or, failing knowledge of these, with the modern name. Some sites, known primarily through an individual archaeological survey, are labelled with their survey inventory number. In areas where entities with no known modern nor ancient name are common -- for example, small villas in Roman North Africa -- no label is used at all for the "nameless" sites.

An entity may have zero or more Geometries

The Barrington Atlas provides only a single geometry (set of coordinates) for most entities. In a few cases, however, multiple geometries are provided, as follows:

  • Some very large settlements, such as Rome, are indicated as points on smaller scale overview maps, but the same settlements are given polygonal "urban sprawl" areas on larger scale maps
  • A few entities (primarily coastlines) are given different geometries at different time periods, e.g., the Mediterranean coastline at the Maeander river delta

An entity is associated (certainly or uncertainly) with one or more Time Periods

The Barrington Atlas makes this distinction. Such associations indicate the entity's period of activity, pertinence or currency. Periods of attestation for a given name are indicated via separate associations with the entity's Geographic Names.

Technical Implementation Details

The Geographic Entity and its components are implemented in Plone via the Pleiades Entity Product.

The following diagram uses the conventions of the Unified Modeling Language (UML) to illustrate the key points made in prose, above. Implementation details, including the specific data fields comprising the Geographic Entity, are best reviewed via the detailed Geographic Entity UML model.

For some of the associations and data fields, thesauri of legal values (also known as "controlled vocabularies") are employed to assist users in data entry and to ensure uniformity of data. For more information on this topic, see: Vocabularies.

Subordinate ContentTypes include:

Design Questions

  • There is precedent in the BAtlas for temporal names and a limited number of temporal geometries. Are temporal geometries an essential aspect?
  • Are there other qualifications that should be applied to individual geometries associated with a single entity?

Notes

We have preferred to use the title "Geographic Entity" over the common GIS term "Feature" because the latter implies, for many people, a single record in a GIS dataset having one and only one geometry. Because of the historical, and therefore often fragmentary, nature of our dataset, we need to place the conceptual idea of space or place above toponomy and location.

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