The middle of a world map is a choice

What is a central meridian?

The central meridian is the line of longitude placed at the horizontal middle of these world maps. A Greenwich-centered map uses 0°. A map centered at 150° east places much of the Pacific and neighboring land near the middle instead. It is a projection parameter, described in the PROJ Equal Earth reference.

Longitude repeats around the globe. A flat world map needs a place where the picture ends and resumes at the other edge. With the three projections here, that cut lies opposite the central meridian. Moving the center therefore moves the cut too. You gain continuity in one part of the world by separating another part.

Why can one country appear on both edges?

A country or island group crossing the cut can appear as two pieces at opposite sides of the map. The geographic object remains continuous across that line on the globe. The split is a consequence of displaying a periodic surface in a finite frame, not a missing or additional territory.

Russia and Pacific island groups make useful examples. Shift the map’s center and watch the split move. If an explanation concerns connections across the Pacific, a Pacific-centered map can keep those connections away from the edges. If the subject concerns another region, a different center may be easier to read.

This is distinct from panning. Panning moves the current drawing across the screen; it does not change its coordinate rule or cut. Changing the central meridian reprojects the geographic data and changes where the cut occurs.

Does a different center change area?

The underlying area figure stays fixed. A longitudinal rotation changes position without adding or subtracting surface. On Equal Earth, the total filled area of a region also stays fixed at a common map scale, even when the outline changes shape or is split into pieces at the cut.

There are two easy sources of confusion. First, independently fitted pictures can have different display scales; compare equal-area figures only when their scales match. Second, a screenshot can crop part of a region. The visible part of a cropped outline is not the complete region’s area.

The interactive map keeps a fixed boundary-model area in the selected-place details. It does not infer that number from the visible portion of the screen. You can use the number as a check while moving the center or zooming into a coast.

What does south-up change?

South-up turns the map so that south is at the top. In this site’s implementation, the projected world is rotated by 180° in its plane. Distances in that drawing and its filled areas stay the same; their positions and visual orientation change. The labels and controls remain readable.

North-up is familiar to many readers, which makes it a useful default. A south-up map may draw attention to that convention or better suit a particular composition. Neither orientation creates an inherently more accurate area calculation. Keep an orientation cue visible when readers could otherwise misinterpret the picture.

Try a deliberate change of perspective

Open Map settings on the home map, choose Pacific, and compare the positions of the outer edges with the Greenwich view. Then switch orientation. Change one option at a time so you can identify which effect belongs to the center and which belongs to the rotation.

For a document or slide, use the map maker to choose the same center and orientation. Review the final crop and labels before exporting. The most useful center is the one that lets the reader see the relationships your map is meant to explain.