Much of the text of Wallace’s book was republished in 1700 in a second edition entitled “An account of the islands of Orkney” but this contained a new map of Orkney. Comparison of this map with others available at that time gave a 99% correlation of its errors with those of the main Collins map clearly indicating that the new “Wallace” map was based on the Collins survey (Table 5). No such match was found with the maps by Adair and Keulen.

These observations were substantiated when a comparison was made of the spelling of selected place names across the maps published between 1680 and 1790  (Table 6). Eighty one  percent of  the selected names present on both the Collins and Wallace 1700 maps were spelt the same compared with 3, 39 and 22 percent for comparisons of the Wallace map with Adair, Wallace 1693 and Keulen. However, Sibbald published a map of Orkney  in 1711 in “Description of the Islands of Orkney and Zetland” which shows an error correlation of 87% with the Adair chart.

Subsequent to the publications referred to above, a county map of Orkney was published by Herman Moll in 1725. Comparison of the errors on this map with those of Collins gave a correlation of 98% (Table 5) and a coincidence of place name spelling of 69% (Table 6). Since Moll is credited as the engraver on Collin’s chart of Orkney, it is not surprising that this chart and Moll’s subsequent map are closely related despite an intervening period of 30 years. However, this does serve  to help validate these techniques  as measures of the relatedness of maps. Interestingly, Moll added a scale of longitude (west of London) not found on the earlier maps based on Collin’s survey.

Orkney 1680 - 1790 (2)

The year 1693 also saw the publication of another map of Orkney in the first edition of the Rev. J. Wallace’s “A Description of the Isles of Orkney” published posthumously by his son Dr J. Wallace . Dr Wallace attributed the map to his father. However, the description of Orkney appears to have been prepared by the Rev. Wallace at the request of Sir Robert Sibbald and to have been based on a manuscript by Robert Monteith dated 1633. Monteith was laird of Egilsay with land holdings in other regions of Orkney. It is thus possible that Wallace’s map was actually prepared by Monteith from his own observations and any access he may have had to the Mercator/Ortelius maps. Such a provenance would predate the publication of even the first map based on Pont’s survey. This could explain why the map was much less accurate when published at the end of the 17th century than those based on contemporary surveys.