Introduction to Maps

By the end of this lesson, students will be able to (per CED LO IMP-1.A):

• Identify the two broad categories of maps (reference maps and thematic maps) and give two examples of each.
• Identify at least five types of spatial patterns shown on maps: absolute and relative distance, absolute and relative direction, clustering, dispersal, and elevation.
• Distinguish between the five most-tested thematic map types: choropleth, isoline, dot density, graduated symbol, and cartogram.
• Explain why every map projection distorts at least one of four properties (shape, area, distance, direction), and identify which property is preserved by the Mercator, Robinson, Peters, and Goode projections.
• Critique a given map by identifying what it includes, what it omits, and what its choice of projection and classification implies.

A map is a flattened, scaled, selective representation of part of Earth's surface. Two phrases in that sentence do most of the work: flattened (you cannot wrap a sphere into a rectangle without distortion) and selective (every map highlights some features and omits others). Geographers organize maps into two broad categories.

Reference maps show general spatial information — where things are, what they are called, and how to get from one to another. The political map on a classroom wall, a road atlas, a topographic map of a national park, and a satellite-imagery basemap on a phone are all reference maps. They are designed to answer "where is X?" or "what surrounds Y?"

Thematic maps show one specific theme or pattern. They are designed to answer "how does this variable distribute across space?" The five most common types on the AP exam:

• Choropleth — areas (countries, states, counties) shaded by a color ramp keyed to data values. The classic GDP-per-capita-by-country map.
• Isoline (or isarithmic) — lines connect points of equal value. Topographic contour lines and weather-map isobars are isolines.
• Dot density — one dot represents N people, events, or objects. Each dot is placed where the underlying feature occurs.
• Graduated symbol — symbols (usually circles) sized by the value at each location. A map of city populations with bigger dots for bigger cities.
• Cartogram — geographic areas resized by the data. The famous "world map by population" stretches India and China into giant blobs and shrinks Russia and Canada to slivers.

Per CED EK IMP-1.A.2, the spatial patterns these maps reveal include absolute distance (precise units like 4,213 km), relative distance (a vague description like "a long flight"), absolute direction (compass bearings), relative direction ("downstream"), clustering, dispersal, and elevation. Every map you read is some combination of these.

The hardest concept in this topic is projection distortion (CED EK IMP-1.A.3). Earth is a sphere; a sheet of paper or a phone screen is flat. You cannot move from sphere to plane without sacrificing accuracy in at least one property: shape (whether features look like their true outline), area (whether two regions of equal real-world area look equal on the map), distance (whether the map's measured distances scale uniformly), or direction (whether compass bearings are preserved). Every projection picks its trade-offs.

Per CED EK IMP-1.A.1, "types of maps include reference maps and thematic maps." Below are examples of each.

Per CED EK IMP-1.A.3, "all maps are selective in information; map projections inevitably distort spatial relationships in shape, area, distance, and direction." Four projections cover most of the AP exam.

Four cases that show how the choice of map shapes the message.

Greenland

2.17 million km² · Mercator inflates ~14×

The textbook Mercator-distortion case. On a Mercator map Greenland looks larger than Africa; in reality Africa is roughly 14 times larger. The high latitude is what stretches it.

Country page →

Democratic Republic of the Congo

2.34 million km² · Equatorial

DRC sits on the equator and shows up at near-true scale on most projections. A useful "control" country to compare against Mercator-distorted Greenland: they are nearly identical in real area.

Country page →

China

1.41B people · Cartogram giant

On a population cartogram, China balloons into one of the two largest "blobs" on Earth (alongside India). On a land-area map it is the world's third-largest country. The two maps tell completely different stories.

Country page →

Australia

7.69 million km² · Continental

Australia is roughly the size of the contiguous United States — a fact that surprises students because most classroom maps use Mercator, which understates Australia and exaggerates the US (the US sits further from the equator).

Country page →

1. The Mercator projection distorts area severely at high latitudes. Why has it remained the default for web maps (Google Maps, Apple Maps) when better-area-preserving alternatives exist?
2. Compare a choropleth map of US median income by county to a dot density map of the same data. Which gives a more accurate impression of where wealth concentrates? Why?
3. Per CED EK IMP-1.A.3, every map is selective. Pick a map you have seen recently and identify what it included, what it omitted, and how those choices shape its message.
4. Cartograms violate basic geographic intuition (they make countries look the wrong size). What do they accomplish that a choropleth cannot, and where do they mislead?
5. Topographic maps use isolines to show elevation. What other variables work well as isolines, and which variables would isolines mislead?

Per CED EK IMP-1.A. Click any term to see the full glossary entry.

Draft alignment — pending educator review. AP HG codes correspond to the official College Board Course and Exam Description (Effective Fall 2020, V.1). Statements below are paraphrased in CountryReports' own voice; refer to the College Board's published CED for verbatim wording.

AP® and Advanced Placement® are registered trademarks of the College Board. The College Board was not involved in the production of this material and does not endorse it. Standards statements above are paraphrased; codes refer back to the official College Board CED, the NCSS C3 Framework, the Common Core State Standards, and other cited frameworks.