Goode’s Homolosine map projection in AP Human Geography

The flattening problem Goode set out to fix

A globe is a curved surface, and there's no way to lay it flat without stretching or tearing something. Every projection has to pick which properties to protect and which to bend.

That's the core idea of Topic 1.1, Introduction to Maps and Types of Maps, in Unit 1: Thinking Geographically. The course states that all maps are selective and that projections inevitably distort spatial relationships in four ways: shape, area, distance, and direction. Goode's Homolosine is the clearest case of a projection built around protecting one of those four, which is area.

How Goode stitched two projections into one map in 1923

John Paul Goode, a geographer at the University of Chicago, introduced the projection in 1923. He combined two existing equal-area projections. The sinusoidal projection handles the low latitudes near the equator, and the Mollweide (also called homolographic) projection handles the higher latitudes. The name "homolosine" blends those two names.

The two pieces meet at roughly 40 degrees north and south latitude. Because both pieces are equal-area, the combined map keeps relative sizes accurate.

Then Goode interrupted the map, cutting it into lobes. The cuts run mostly through the oceans, which reduces distortion across the major landmasses. Some land areas still get split, though. Antarctica, for example, ends up in pieces. The lobed layout is why the map looks like a peeled orange laid flat.

What the cuts cost: shape, distance, and direction

Because it's equal-area, Greenland shows up at its real size compared with Africa, which is much larger. Russia, Canada, and Antarctica also stop looking oversized.

The trade-off shows up in three places. Shapes stretch and bend toward the outer edges of each lobe. Oceans get sliced apart, so you can't trace a straight route from one side of the Pacific to the other. Distances and compass directions aren't consistent across the map, which makes it useless for navigation.

Keep in mind that equal-area doesn't mean distortion-free. Goode's still distorts three of the four properties. It just keeps the one that matters most for comparing regions.

Reading a global data map built on Goode's

World thematic maps often use equal-area projections because the size of a shaded region shapes how big a pattern looks. If a choropleth map of population density were drawn on a projection that inflates high latitudes, Canada and Russia would look like huge blocks of low density and pull your eye away from the dense clusters in South and East Asia. On Goode's, the visual weight of each region matches its real area.

On the exam, this applies to stimulus-based multiple-choice questions that show a world map, and to Question 2 (One-stimulus question) or Question 3 (Two-stimuli question) when the stimulus is a global map. The skill is matching a projection to its purpose. A strong answer names the property the projection preserves (area), names what it distorts (shape, distance, direction), and explains why that fits the data shown, such as comparing land use, population, or climate regions across continents.

Goode's vs. Mercator: the swap to avoid

These two answer the same problem in opposite ways, so they're easy to flip. Mercator is a rectangular, continuous projection that keeps local shapes and constant compass bearings, which suited sailors, but it badly inflates areas toward the poles. Goode's keeps area true and gives up continuity and shape.

Here's a quick way to sort them in a question:

• Comparing sizes of regions or mapping global data: Goode's Homolosine
• Navigation or a straight line of constant compass direction: Mercator
• Maps centered on a pole, such as Arctic routes: a polar projection

One more trap is assuming that the gaps in Goode's map are a flaw or missing data. The interruptions are deliberate. They help reduce distortion over land, while the equal-area projections underneath preserve relative areas.