Regional data compilations
West Greenland (66°-70°15') - the Palaeoproterozoic Nagssugtoqidian, Rinkian Orogen and the adjacent North Atlantic Craton

Topography, Entire Greenland Geological environments and related Mineral Occurrences
The geographical position of mineral occurrences comes from different sources
(reports, readings from old maps and GPS positions) and therefore some positions
may fall outside land areas of the geological map based on G/2.5 M Vector topographic
data from KMS/GEUS 1997 (KMS = Kort & Matrikel Styrelsen = National Survey of Cadastre).

Topography, West Greenland (66°-70°15')
The geographical position of mineral occurrences comes from different sources (reports, readings from old maps and GPS positions) and therefore some positions may fall outside land areas of the topographic base 1:250 000 used here.

The geological map is based on G/2.5 M Vector topographic data from KMS/GEUS 1997 (KMS = Kort & Matrikel Styrelsen = National Survey of Cadastre) and therefore does not align to the topographic base 1:250 000 used here. The present topographic area covers West Greenland from 66°00' N to 70°15' N and comprises c. 51 000 km² ice-free land area. The GGU/GEUS laboratory produced digital topog-raphic data covering the area during the period from 1986 to 2001.

The topographic data have been grouped into subsets reflecting that the quality of the ground control of the photogrammetric methods have improved over the years (Fig. 1). Aerial photography from c. 14 km altitude with super-wide-angle 9-inch photogrammetric cameras (giving a nominal scale of 1:150 000) was carried out by KMS in 1985 and 1987 and is the basis for all map productions.

Ground control was also established by KMS. From 1976 the TRANSIT satellites and Doppler measurements and later GPS measurements were used at a number of geodetic control points to strengthen the traditional trigonometric network. The network was tied to the reference frame WGS84.

A large part of the area is aerotriangulated by KMS. In each aerial photograph 10+ points are measured, each of which are measured in 2 – 4 different overlapping photographs. The location of the geodetic ground control were visually transferred to the photographs and included in the point measurements. The observations were computed in a least squares adjustment (Poder, 1982), with each photo treated as a free bundle of rays. The adjusted xyz-ground coordinates have root mean squared (rms) errors better than 10 m.

The time-consuming measurement of the many photos covering all of Greenland lasted some 25 years. Approximately 50% of the project area was aerotriangulated by the GGU laboratory using photogrammetric model coordinates as computational units. The resulting GGU-generated ground coordinates have xy-rms errors of app. 30 m and z-rms errors of app. 10 m.

Up to 1999, a mechanical-optical 2nd order stereo-restitution instrument of the type KERN PG2 using transparent photographic copies of the aerial photographs produced the topographic data from the GEUS laboratory. Both the hydrographic themes (coastlines, lakes, rivers, ice margins) and the contour lines were generated manually. In the period up to mid-1988, the PG2 instrument were equipped with a slow prototype xyz-digitiser which time and again would skip one or two vertices when the stereo-operator was drawing with at high speed.

Index map showing topographic data subsets. GGUPG2 = PG2 data based on GEUS aerotriangulation, KMSPG2 = PG2 data based on KMS aerotriangulation and KMSDPW = DPW data based on KMS aerotriangulation. Map from Schjøth & Steenfelt (2004).

From 2000 and onwards topographic data has been produced by a digital photogrammetric workstation (DPW) from LH-Systems using digital scanned copies of the aerial photographs. The hydrographic themes are still generated manually whereas the contour lines are generated from an automatically extracted digital terrain model (DTM). Breaklines in-cluding the hydrographic themes are included during the DTM generation.

The raw 3D photogrammetric data (at scale of 1:100 000) are exported to the Esri ArcInfo GIS-platform as 2D data. The topology is validated (i.e. polygons are closed) and attribute data are added. In a semi automatic procedure the 1:100 000 data are generalised to a 1:250 000 version using line smoothing, elimination of small areas and minor rivers. Data at the two target scales are each unified in to seamless data sets.

The projection parameters are:

	Geodetic reference:	WGS84
	UTM-zone:	22 (i.e. the central meridian is 51° West)
	False Easting:	500 000

The copyright for topographic base data in scales 1:250 000 belongs to GEUS and shall be notified as follow:

Topographic base:

copyright GEUS 2003

The base map used for the geoscience data is based on the G250 Vector digital topographical map in scale 1 : 250 000, produced jointly by National Survey & Cadastre / Kort- og Matrikelstyrelsen (KMS) and GEUS in a project financed by the Bureau of Minerals and Petroleum (Minerals Office 1997). The vectorised map data are based on the printed maps as published by KMS, or where ossible, on newer photogrammetric maps in scale 1 : 100 000. The original maps are in a Lambert conformal conic projection. The scanning and digitisation process therefore involved a fitting of the data to the modern standard Universal Transverse Mercator projection (UTM) for this region of Greenland by 'warping' the scanned and digitised map data to fit triangulated geodetic control points. In general, such a process is not accurate, but produces a digital map in UTM, which though on average better than the original map, still contains significant errors in the position of individual features of the map. Also, the process does not correct the position of features erroneously
located on the original map. This can be seen locally in South Greenland, e. g. by comparing the topographic base map in line form with the satellite map.