Spatial Reference System
QGIS asked me for the CRS/SRS (a combination of map projection and datum, CRS = Coordinate Reference System) when I opened the files. I tried first with the commonly used global EPSG:4326 and EPSG:900913 but it looked distorted. Without a proper base map, it was hard to determine, so I went ahead and found an open web map service first and showed the data on top in various projections (see the section later about this). I used to work as a GIS expert and developer in Denmark and The Netherlands respectively. In DK the most common SRS was EPSG:25832 while in NL it was EPSG:28992.
I’ve built up a network of Norwegien GIS professionals over Twitter, LinkedIn and Facebook, so I threw the question out there:
Before long, I had several answers saying that EPSG:25832 and EPSG:25833 are the most widely used in Norway. Once I had a base map in place, I was able to verify, that EPSG:25832 was the correct projection.