PRESUMABLY ALL READERS of The Map Collector, whether scholars, collectors, curators, dealers or just plain cartophiles, have been frequently faced with the problem of assigning an undated map to a plausible period. Different situations call for different approaches. If you are lucky, somebody else has already done the work and it is just a matter of running the right bibliographical or cartobibliographical reference to earth. Following biographical leads can be particularly rewarding. Information about the careers of surveyors, mapmakers, engravers and publishers often helps to pare away at the lunatic fringes of dating suggestions. Not that the literature is free from instances of cartographic geniuses who apparently produced work before their tenth birthday and others who continued hale and hearty decades after their death.

Heraldry, whether personal or national, and the portraits of dignitaries that typically embellish seventeenth century maps, are always worth checking out. Watermarks, except when they incorporate a date (as with Whatman paper from about 1790 onwards), tend to offer more problems than solutions. Booksellers' catalogues and newspaper advertisements remain valuable, if underused sources. Chronograms (disguised dates formed of jumbled-up Roman numeral letters) occasionally occur on maps. The context in which a map is found (particularly if a manuscript) can often provide pointers to date, as can its provenance. The art-historical approach, or the layman's, 'it feels early eighteenth century', rounds off this very summary and incomplete list of the possible ways of attacking an undated map.

As will probably have been noticed, the previous paragraphs were concerned with peripheral elements, not with the map's core, its cartographic content. To provide a structured chronological index to that content is the primary aim of the Cartochronology Project, launched at the Eleventh International Conference on the History of Cartography in Ottawa last July.

There is nothing remotely original in the use of internal evidence to fix one side of the possible time bracket for an undated item. If, for example, a map names Savannah in Georgia, it can be confidently dated after the town's foundation in 1733. The corollary, that any map lacking Savannah must predate its creation, is unjustified, however. Allowance always needs to be made for cartographic time-lag and for the copying of copies. But a terminus a quo, a 'later-than-date', does at least give one fixed point. To find a specific piece of information, like Savannah's foundation date, is easy enough and the history of cartography is littered with dating estimates obtained in this way. But even if many local or regional historians have an encyclopedic knowledge of their own area, they seldom publish a chronology for others to use. Are they always sure, indeed, exactly which of the several hundred names on an average map emit dating signals? To search in a gazetteer (usually arranged in dictionary order, not by area or date) involves a ruthless pre-selection, given the number of possibly relevant place-names. Those chronologies that do exist have been prepared for other purposes and list little information that is likely to show up on maps.

So the Cartochronology Project was conceived. It is designed to be an international pooling of specialist regional knowledge, complemented by systematic searches through a wide range of reference sources. Its aim can be simply expressed: to provide on a regional basis, separate chronological lists containing all types of information that might help to date the content of any sort of cartographic document. Its exclusive concern with content needs to be underlined.

No information that tended towards this end would be spurned but it is anticipated that the entries will be of two main types, each with subsidiary elements. First would be changes in man's knowledge of the world or perception of it, through discovery, exploration, or theorising. Respective examples would be Le Maire's discovery in 1616 of the Cape Horn passage and of the strait named after him, the exploration of the Coppermine River in northern Canada by Hearne in 1771-2, and the mistake which turned California into an island on maps produced after 1622. Topographical or hydrographical surveys could also be recorded if they are precisely datable, provided they can be described or illustrated.

Greenville Collins' chart of the Scilly Isles shows how biographical information can help date a map. Certainly used in its original 1693 form by the British admiral Sir Cloudesley Shovell, its later versions mention his shipwreck in 1707 as can be seen in this detail from the lower edge of the chart (By courtesy of the British Library).


Probably the biggest of the man-made alterations that show up on maps produced between 1500 and 1900 were the Dutch drainage schemes of the early seventeenth century. On this 1630 Hondius map of North Holland a number of polders (reclaimed areas) can be made out: Zijpepolder (drained 1597), Beemster (1607-12), Purmer (1617-22) and Wormer (1624-6). De Waert (1625-31) is shown partially reclaimed, but not Schermer (1631-5) (By courtesy of the British Library).


It is the foundation and spread of settlement that offer the greatest choice of datable facts. Fort Kasimier, built by Peter Stuyvesant on the Delaware River in 1651, was added to the second state of Visscher's map of New England, but the presence of Philadelphia, also shown on this detail, provides a 'later-than' date of 1682, when the Quakers started laying out their city (By courtesy of the British Library).

The second broad category of datable cartographic information would concern alterations to the real world through natural events or man's activities. Instances of the less usual first element might be documented deviations in river courses and, specifically, the eruption of Krakatoa in 1883. The second element, the developing human geography of our planet, will certainly provide the lion's share of datable cartographic features. Changes to a country's actual shape, as brought about, for example, by Dutch reclamation schemes, are noteworthy but exceptional. The most prolific source for the Cartochronology will undoubtedly be the foundation and spread of settlements, like the Savannah example already mentioned. This will apply especially to the regions beyond Europe, where the pioneers arrived within relatively recent history.