[NUUG kart] N50 imports from Kartverket (The Norwegian Mapping Authority)

Tor Mehus torsm.news at gmail.com
Fri Jun 13 00:01:29 CEST 2014

Hello everybody,

Several people around Norway have started importing data from the N50 Kartverket data sets. DWG member Paul Norman contacted me because I was one of those who had imported N50 data. He brought to my attention that these imports have been carried out without the required consultation on the OSM imports mailing list first.

In September 2013 the Norwegian Mapping Authority (Kartverket) released various data sets under an OSM compatible licence (CC BY 4.0; <http://www.kartverket.no/Kart/Gratis-kartdata/Lisens/>).

OSM coverage in Norway varies from good to excellent in major cities to very sketchy and imprecise in many rural areas (with huge white spaces on the map). Norway is very scarcely populated, and we can't rely on manual edits alone if we want to map the entire country. The data that Kartverket has released gives us the possibility to raise the quality of OSM in Norway considerably.

This e-mail concerns imports from the N50 data sets in particular. It does not deal with imports from other data sets from Kartverket, such as Vbase or SSR.

N50 is a collection vector data sets used for producing topographic maps (typically 1:25 000, 1:50 000 or 1:100 000) for both civilian and military use. N50 is used as the main data source for almost all topographic paper maps published in Norway. It is also used for producing electronic maps, such as the Garmin topo maps.

In general N50 data is of high quality, although some features are exaggerated for rendering purposes.

Information about import procedures can be found at the Kartverket imports wiki page: <https://wiki.openstreetmap.org/wiki/No:Kartverket_import>.

The wiki page is a work in progress and will be expanded.

N50 data is available for download  from Kartverket in SOSI format (divided by municipalities) or in geoJSON format (whole country).

A description on how to convert data from SOSI is given on the wiki page.

The wiki page contains a list of the map features that are imported.

The wiki page also briefly describes what should not be imported from N50, either because the data is not appropriate for OSM (e.g. contour lines), because it is imported from other sources or data sets (e.g. place names from SSR or roads from Vbase) or because the N50 data is considered to be too inaccurate or outdated (e.g. footpaths).

Kartverket has made available a product specification for N50: <http://www.statkart.no/Documents/Kart/N50-N5000%20Kartdata/Produktspesifikasjon%20N50%20Kartdata%20versjon%20mars%202014.pdf>.

The specification should be consulted before a decision is made to import features not already described on the wiki page.

This is a community import.

Only experienced mappers are encouraged to import data.

Data is available in SOSI and geoJSON formats requiring conversion before import. Although it does not automatically guarantee that people understand the technicalities of OSM, the conversion process in itself requires at least a minimum degree of technical insight.

The N50 data sets contain huge amounts of data. Mass imports are discouraged. People are encouraged to import only small amounts of data at a time, and only after validating the data and correcting errors.

Only OSM tags are to be used. All Kartverket tags are either removed or changed to OSM tags before import.

All changesets and imported elements shall be tagged:

Tagging guidelines are given on the wiki page.

Only features that can be tagged with appropriate OSM tags are imported.

As a general rule, existing data is kept. Data should only be imported if it does not already exist or if it is of better quality than existing data.

Conflicts with existing data should be sorted out before importing. If in doubt, surveying on the ground should be carried out or other sources, such as Bing imagery, consulted before existing data is replaced.

In cases where imported data is used to replace existing data, importers are encouraged to "replace geometry" if possible, thus retaining as much as posible of the edit history.

In many places in Norway (especially rural areas), conflicts with existing data are unlikely to become an issue because there either is no data at all, the particular element is missing in OSM, or because it is evident that the element in OSM is of much lower quality (e.g. a square lake).

The N50 import process has been discussed on the regular Norwegian OSM community mailing list <kart at nuug.no> (<http://wiki.nuug.no/grupper/kart>).

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