Thomas Hans Henrik Knoff was a Norwegian Army surveyor. In the year 1730 he was sent to Iceland by the Danish government to continue and complete the work of Magnús Arason who had been instructed to survey the whole of the country but died before the work was finished. The purpose was to make a precise map of the country once and for all.
Knoff began work immediately after his arrival in Iceland and carried on for five summers. He had by then completed the work left undone by Magnús and corrected his maps to some extent, where it seemed necessary. He had also made seven maps of specific districts and an overall map of the whole country which he finished in the year 1734. When the maps were brought to Copenhagen an amazing dispute began over them. Knoff had sent a copy of some of them to his superior in Norway. Some regarded this as quite outrageous if not actually treasonable. The Danish king put an end to the dispute by deciding that the maps should not be displayed or made use of. Their fate was thereby decided, and they were put away under lock and key in some government department, where they lay unpublished and forgotten by nearly everyone for many years.
The maps of Magnús Arason and Knoff mark a turning-point in the cartography of Iceland. For the first time an attempt is made to produce a map of the country by means of measurements of latitude and longitude and triangulation.
In 1752 the Danish scholar, Niels Horrebow, published his book about Iceland. It is accompanied by a map of the country based on the map by Knoff which had now been brought out of some cabinet and dusted off. The map is altogether rather careless and poorly done.
In 1750 Otto Manderup Rantzau became prefect of Iceland. He made it his business to have the Knoff map published in a better and more accurate version than Horrebow's, and turned for this purpose to the most distinguished firm of map makers in Europe at this time, Homanns of Nürnberg.
The map appeared in 1761 with a prodigiously long name in Latin giving details of its origin. It is reduced by more than a half from Knoff's original. In content it is for the most part unchanged and includes almost everything of significance. The text is translated into Latin or German or even both. Place-names are slightly pruned, and their treatment absolutely wretched. Someone, apparently with a slight knowledge of Iceland, probably went over the map before it was printed, to judge from occasional corrections, additions, and new passages of text. The Homanns map also seems to have borrowed some material from the county and regional maps of Magnús Arason and Knoff, though it does not amount to very much.
The Homanns map of Iceland seems to have been printed as a separate sheet and never incorporated in their atlases. And only one edition is known.