0

I have a shape file with projected coordinates specified in Canada Atlas Lambert (NAD83) (ESRI:102002) and have been trying to convert the coordinates to lat/long (ideally in WGS84). However, whenever I do the conversion the map coordinates near the top of the map seem to disappear and the shapes continue straight to the edge of the map.

Notably, the map is of northern parts of Canada which seems to be the cause for the distortion.

Is there a way to properly convert the projection to coordinates? I've tried proj4 and QGIS with no luck.

5
  • 1
    How are you converting them now? QGIS > export as shapefile > set CRS on export is the best option. Is the data available publicly? – DPSSpatial_BoycottingGISSE Mar 27 '20 at 22:09
  • Hm, if you do a conversion "back" into lat/lon, there should not be a distortion, because lat/lon can't leave their coordinate window (extent). Can you check the extent of you lat/lons? – Andreas Müller Mar 27 '20 at 22:58
  • @DPSSpatial I've been attempting to convert/export them as GeoJSON, setting the CRS to WSG. It works, and in QGIS it still looks fine, but when I map it anywhere else the top goes off. The data is public, but may need an account to download, this should be a direct link: geomatics.gov.nt.ca/Membership/dls/BNDCFG_ENRITI_ADMIN.zip – Programming123 Mar 28 '20 at 6:31
  • @AndreasMüller What am I checking for Extent wise? I've tried it to ways calculated from Layer (N: 5848258.6848, E: -487.5008, S: 2248971.2600, W: -1637326.1638) and from the Canvas extent (NL 6595215.3910, E: 5122179.3220, S: 1456183.1622, W: -4492572.7546). – Programming123 Mar 28 '20 at 6:36
  • Those are not wgs coordinates. – Andreas Müller Mar 28 '20 at 9:06
1

The .PRJ in the shapefile isn't being read correctly.

If you load the shapefile into QGIS, manually set the layer CRS (not the map) to:

EPSG: 102002 (Canada_Lambert_Conformal_Conic)

Once the layer has a valid coordinate system, you can re-projected it to WGS84 / EPSG 4326 as you export to GeoJSON.

4
  • I tried loading the .SHP file, then set the CRS on the layer to EPSG:102002 and saved it as a GeoJSON. When I have it added to the map within QGIS is looks alright as an extra layer, but when I import it thorugh mygeodata.cloud or onto a map in leaflet it still has the same northern distortion. Any idea what's happening? – Programming123 Mar 28 '20 at 22:42
  • Looking back at it, it appears that one line connecting two points is not being drawn, and instead the shape then fills up to the top of the map from those two points. Could there be something missing that's making the polygon not include that one line? I only noticed this because Google Maps also does not draw that same line. – Programming123 Mar 28 '20 at 22:47
  • 1
    @Programming123 it could be some corrupt geometry at the very top of the data, which is close to the poles. Perhaps you could just cut the top off and re-create the 'top' of the data, or run some geometry validation tools on it in qgis... – DPSSpatial_BoycottingGISSE Mar 28 '20 at 23:39
  • WebMapping-Applications often use the Google Projection (web mercator), which has a huge distortion towards the poles. so, if your data is north of 85.051129° some applications cut those areas. Please check, if this is true for you. – Andreas Müller Apr 2 '20 at 8:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.