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GIS newbie at a loss for solutions here.

I've drawn and mapped out a shapefile with 51 features in QGIS based on administrative region data which has been in EPSG:4326. I would now want to convert this data to EPSG:3857 while maintaining the same lon/lat values. However, when trying to convert it, my coordinate extents become

-17336426.8035119101405144,-3669673.3683910621330142 : 19156980.9545540697872639,6001856.2008783714845777

which are not the same. I've tried QGIS's reproject layer tool and an R script

library(sf)
shape <- st_read("/Users/eulinean/country/country.shp")
reproj_shape <- st_transform(shape, "+init=epsg:3857")
st_write(reproj_shape, "/Users/eulinean/country/reproj_country.shp")

to do this. I think there's something obvious I'm missing here but I can't figure out what. Is it possible to do this?

Shapefile properties before reprojection:

Information from provider

Storage
ESRI Shapefile
Encoding
UTF-8
Geometry
Polygon (MultiPolygon)
Extent
-155.7357716961408869,-31.2838943163903451 : 172.0900878906250000,47.3650000000501734
Feature count
51


Coordinate Reference System (CRS)


Name
EPSG:4326 - WGS 84
Units
Geographic (uses latitude and longitude for coordinates)
Method
Lat/long (Geodetic alias)
Celestial body
Earth
Accuracy
Based on World Geodetic System 1984 ensemble (EPSG:6326), which has a limited accuracy of at best 2 meters.
Reference
Dynamic (relies on a datum which is not plate-fixed)

and after:

Information from provider

Storage
ESRI Shapefile
Encoding
ISO-8859-1
Geometry
Polygon (MultiPolygon)
Extent
-17336426.8035119101405144,-3669673.3683910621330142 : 19156980.9545540697872639,6001856.2008783714845777
Feature count
51


Coordinate Reference System (CRS)


Name
EPSG:3857 - WGS 84 / Pseudo-Mercator
Units
meters
Method
Mercator
Celestial body
Earth
Accuracy
Based on World Geodetic System 1984 ensemble (EPSG:6326), which has a limited accuracy of at best 2 meters.
Reference
Dynamic (relies on a datum which is not plate-fixed)
eulinean
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    You would expect the coordinates to become much larger with that transformation, why do you think they are wrong. – Ian Turton Jun 05 '23 at 12:21
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    You can't project a dataset in degrees (+/-180,+/-90) into Web Mercator meters (+/-somethinglarge, +/-infinity) and keep the same unit values. If you accomplished your goal, you'd be mapping on "Null Island". – Vince Jun 05 '23 at 12:23
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    One degree at the equator has an East-West-extent of about 110 km, or 110,000 m. Therefore a m-based CRS must sport way larger X- and Y-values than a degree-based CRS. – Erik Jun 05 '23 at 12:32
  • Thanks all. I thought it must've been something fundamental I was missing. If it isn't possible, I'll try to re-do things starting with the correct projection. – eulinean Jun 05 '23 at 12:46
  • Welcome to Geographic Information Systems! It looks like you have a coordinate system problem, see if any of the suggestions at https://ihatecoordinatesystems.com/ help. – Ian Turton Jun 05 '23 at 14:16
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    if you convert from EPSG:4326 to EPSG:3857 you change the units from degrees to meters and the extent values change accordingly – nmtoken Jun 05 '23 at 17:03
  • See here for background: https://gis.stackexchange.com/questions/383434/changing-shapefiles-from-geographic-wgs84-to-projected-epsg2263-coordinate/383437#383437 – Babel Jun 05 '23 at 18:53

0 Answers0