What is it that a well-defined population exports and imports over the years? The difficulty is to find suitable, limited areas to investigate, where relevant archival sources are preserved.
An area suitable for investigation ought to be an island of provincial size, situated not too close to the mainland coast. There are two reasons for this: 1. A population too small is not representative. 2. If the mainland is too close, the margin of error increases concerning the evidence of legal or illegal trade, for instance smuggling.
Gotland has the right size and location. Moreover, Gotland has an exceptionally comprehensive and well-preserved archival material concerning export and import from a very long period: from the 1620´s until 1963. The material consists of journals of customs duties and harbour dues. Not only foreign but also domestic trade is thoroughly documented. The journals are kept in the Regional Archives in Visby and in the Municipal Archives of Gotland, Visby.
Reliability of the documents
How reliable are these documents? It has been possible to estimate the percentage of smuggling at about 20% at the end of the 18th century. This is according to Robert Bohn, who in his thesis 1989 was able to compare the private accounts of the trading company Donner with the official journals. The journals of customs duties and harbour dues give, as it were, 80% of the truth. In other words, the material offers a satisfactory connection with reality.
It should be emphasized that the data of export and import on Gotland mentioned above are quite unique. There are evidently few other areas that have material from such a long period of time.
Other interesting islands
There are however some islands in Europe which are able to qualify when it comes to size and location: in the Mediterranean mainly Malta, Cyprus, Majorca and Minorca; in the north Atlantic Iceland, Isle of Man and the Channel Islands; in the Baltic Bornholm and Gotland. As for Bornholm, there is unfortunately no suitable archival material preserved.
Of particular interest in this matter are the sources of the Isle of Man. This island has "Ingates and Outgates" even older than the Gotlandic ones. They begin 1594/95 and the records until 1765 are kept on the island, the following years in the Public Record Office in London.
One vision is that certain years of data should be digitalized, which requires considerable resources. Another vision is that different key-studies should be accomplished by smaller groups of researchers. It is important to establish which years of data are represented in more than one area of investigation. The project ought to give priority to such years. On Gotland, and obviously also on the Isle of Man, most years are preserved.
At present one should concentrate on investigating the situation concerning archives and research on the islands of northern Europe.