4

I opened one of the world files from Natural Earth in QGIS. It opens in EPSG:4326 (the default CRS). When I change the projection to Equal Earth Greenwich, it looks fine, but if I try EE Americas or EE Asia-Pacific, I get weird lines in the polar regions (see attached images). What's going on here?

EPSG:4326

Polar

1

1 Answer 1

9

What is going on is that the Natural Earth shapes are crossing the longitude "cut line" at the edges of the map in the projected map.

When centred on Greenwich, the definers of the shapes have made sure the boundary of each one never crosses 180 degrees E/W of longitude, which is the cut line of the top projection.

When you shift to the Asian-centred projection, the Greenland shape, for instance, just crosses the "cut line" at the longitude just east of the east coast of Brazil. The vertices get connected, but when projected are now completely on the opposide sides of the projected map, hence the horizontal line. Ditto for the others.

You didn't explicitly ask for solutions, but if you need one, here's one thing you could do. Double check the cut line of the AP projection; I suspect it's 30 W. Take the shapes of Greenland and Antarctica and cut them into 2 exactly at this longitude, maybe shaving off a tiny bit so it never quite touches that precise cut line. Now each of the 2 shapes should render without lines.

If you want to be super detail oriented, you will notice that there is a vertical line through Chukotka Autonomous Okrug on the extreme east end of Siberia on your AP map. This represents a split of Siberia into 2 shapes in the Natural Earth dataset to avoid those nasty lines in the more conventional Greenwich-centred projection. You could also merge those 2 shapes to remove it in the AP map.

2
  • Thanks for that explanation - I appreciate it. Apr 21 at 0:29
  • 4
    Please accept the answer by clicking the checkmark under the score
    – til_b
    Apr 21 at 8:26

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.