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I opened with QGIS the shapefile in the following archive http://data.openstreetmapdata.com/coastlines-split-4326.zip and I want to convert this shapefile to a list of latitude and longitude values for every coastline point. To do so, I opened the .shp file with QGIS, then clicked on 'lines' on the layer panel, selected 'Save as...', selected the following options enter image description here, and clicked on 'OK'.

I obtain a .csv file that looks like this

"WKT,FID,
"LINESTRING (-4.94237 55.725449,-4.941922 55.725585, ... " 

May you please confirm that the pairs of numbers (e.g. -4.94237 55.725449) correspond to the GEODETIC latitude of a point and to its longitude (both in degrees), respectively?

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Pasting the coordinates in Google Maps does plot a point somewhere in the ocean, and since you are using the coastline shapefile I will assume it's correct. OSM shows thisenter image description here

  • There must be something wrong here, if you zoom in to that point on Google Maps, there is no coastline... – James Feb 22 '16 at 12:36
  • Google doesn't show anything there but you are using the osm coastline data, I am updating the image to one of osm – Hasan Mustafa Feb 22 '16 at 12:54
  • But if you switch them for lat/lon you get google.co.uk/maps/place/… – Ian Turton Feb 22 '16 at 12:55
  • @iant the point still doesn't fall on a boundary, I would think that coastlines would either fall on the boundary between land and water or somewhere in the ocean, not inland, but I'm exactly sure how OSM coastlines work. – Hasan Mustafa Feb 22 '16 at 13:02
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iant, I now remember that the first number is longitude, while the second one is latitude: if you swap the numbers and plot on Google Earth rather than google maps, you obtain that you are right on the boudnary

enter image description here

1

QGIS hasn't done anything to the numbers, so they are probably whatever they claim to be, which is lat-long points using EPSG:4326, which is a lat-long coordinate system based on the WGS84 spheroid.

If you really just want the points, there's probably a "Lines to points" option somewhere in QGIS that will convert your line features to point features, then you can save as CSV with one point per line.

I can't recall if WKT is lat-long or long-lat, but you can easily test this with a few samples...

  • There indeed is a lines to points tool. If the coastlines are polygons you would have to convert to lines before use though. – Kingfisher Feb 22 '16 at 13:18

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