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I am trying to use the global GEBCO grid in an Equal Earth projection (EPSG 8857) in QGIS. However, no matter what I do, reprojecting it or clipping it, QGIS always "adds" these corner parts to the map. For example, this does not happen using a Mollweide projection.

Has anyone an idea how to avoid this?

enter image description here

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    The corner parts are the repeated parts across the 180 line - New Zealand would appear again in the bottom left on this map. Only way I can see to do it is to create a polygon of the edge shape and crop or mask using overlay modes... You don't need to download this data to show this problem, an OSM base map with project CRS set to 8857 has this as well.
    – Spacedman
    Apr 28, 2021 at 14:00

1 Answer 1

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Step 1, create a rectangle in EPSG:4326 around the earth. Don't cross the date line! Here's a simple geoJSON file that goes to 1/100 of a degree:

{
"type": "FeatureCollection",
"name": "box",
"features": [
{ "type": "Feature", "properties": { }, "geometry": { "type": "Polygon", "coordi
nates": [ [ [ -179.99, -89.99 ], [ -179.99, 89.99 ], [ 179.99, 89.99 ], [ 179.99
, -89.99 ], [ -179.99, -89.99 ] ] ] } }
]
}

Save that to a box.geojson text file (mind the line breaks) and load into QGIS.

Loaded and overlaid on an OSM map, with project CRS set to 4326 you'll see it is slightly bigger because OSM only goes to +/- 85 degrees or so:

enter image description here

Now set project CRS to 8857:

enter image description here

The east and west lines cut straight down because we only have four points in that polygon. Use Vector | Geoprocessing Tools | Densify by count and use that dialog to create a new layer with a few thousand extra points on the polygon.

By the magic of PROJ, that polygon should now closely follow the +/- 180 line. Here I've hatch-shaded it:

enter image description here

Next use the styling dialog to colour it white with an "Inverted Polygons" fill:

enter image description here

Remove the line styling if you don't want the black outline. You might be able to use QGIS layer composition options to mask it out in some other way. Group the layers together in the Layers dialog for handy shuffling around.

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  • This works perfectly for my purpose. Thank you!
    – Deepmir
    Apr 30, 2021 at 7:35

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