The North Volcanic Zone of Iceland is clearly aligned from north to south. But Iceland has another axis like that, farther to the west. The two different axis or lines are of the same nature. Actually, the North Volcanic Zone did replace the Skagafjordur Volcanic Zone. Therefore, the distance between the two axis is exactly 3° from east to west, because both axis have their roots in the convection rolls pattern.
The western axis is older, and contains the central polygon of the Icelandic Plateau, where the distance to the edge of the elliptically shaped plateau is the same to the east and west. As shown in other posts, that axis is also centrally located between the main outposts of Icelandic volcanoes, Snæfellsjökull and Snæfell.
We get a geological/geographical bonus by seeing how the glacier Vatnajökull is shaped by the convection rolls framework, as one polygon is colored almost completely white. The other parts of the glacier seem to reach out from that central area. Similar features can also be clearly found for Langjökull, covering the western half of its polygon.