Thematic Maps

How do you make a bunch of statistics more interesting to read? Geographers and cartographers everywhere agree: you turn it into a map!

Thematic maps are a way of visualizing spatial data and can therefore be powerful tools for transmitting information. We'll highlight the characteristics of thematic maps, as well as the major types of thematic maps you're likely to come across and the symbols that go with them. As you read this explanation, think about the importance of the visual representation of information.

Thematic Maps Definition

The word "thematic" may be slightly misleading—these are not the colorful and exaggerated maps you might get in a pamphlet at a zoo or an amusement park. Rather, thematic maps are visual displays of statistical information.

The "theme" in thematic maps is the subject, or theme, of the statistical data. Thematic maps typically have just one, single, defining theme.

Characteristics of Thematic Maps

Most maps have a few core characteristics in common. A map projection tells us how our three-dimensional globe is being displayed on a two-dimensional map and the potential distortion that comes with it. Scale gives us information about the size of the area being displayed. Map orientation tells us which way is north, latitude and longitude help us pinpoint coordinates, legends (or keys) tell us what symbols might mean—and the map title tells us what the map is actually of!

But unlike most maps, thematic maps are useless for navigation. Similarly, while thematic maps may display political or scientific data, they typically display very little conventional information about political geography or physical geography—that is to say, you probably wouldn't want to use a thematic map to figure out the capital of Brazil or learn where the Pyrenees Mountains are.

For this reason, thematic maps are sort of a middle ground between graphs and maps. Like a graph, a thematic map is an easily understandable visual display; like all maps, a thematic map displays information over space. Characteristics of thematic maps include a title; an underlying data set (the theme); a visual display of space; a set of symbols and colors to transit the theme; and a legend to tell you what symbols or colors mean. Things like latitude and longitude or a compass are usually less important on thematic maps, and often they are not incorporated at all.

In the world of human geography, thematic maps are especially good for providing a visual of population-related information, such as population density, concentrations of political or religious beliefs, or ethnic and racial distributions.

Thematic Map Symbols

On a reference map, symbols like a small dark circle may indicate a major city, while a star can indicate a capital city. But on thematic maps, the symbols are not the sideshow: they are often the core element of the map, the conduit through which the geospatial data are being visualized.

Thematic maps use a variety of symbols to display data. These symbols include, but are not limited to:

• Dots

• Proportional circles

• Color variations

• Arrows/lines to demonstrate flow

• Pie charts

Each of these symbols is associated with particular types of thematic maps, which are discussed in detail below.

Types of Thematic Maps

There are dozens of different ways to display statistical data on a map, and thematic maps are widely used in both physical geography and human geography. For the purpose of our discussion here, we will limit our overview to four of the most common types of thematic maps you are likely to come across in AP Human Geography.

Choropleth Maps

A choropleth map is a map that uses colors to show variations in a population. Choropleth maps often shade areas based on legally recognized political boundaries and are useful in showing differences between people living in different areas.

Because they tend to generalize data, one significant disadvantage of choropleth maps is that they may present skewed information (sometimes intentionally!). For example, suppose a choropleth map compared the political leanings of people across the United States based on state borders. You might get the impression that a widespread majority of a state has a particular political leaning, when in reality, that political leaning may be concentrated in just a few highly-populated counties or cities within the state. For this reason, choropleth maps may sometimes use additional political boundaries (like county lines) to present a more accurate picture.

Choropleth maps are extremely common—arguably the most common type of thematic map. It is likely that you run into choropleth maps on a daily basis if you watch or read the news. You may have even seen some choropleth maps in other articles here on StudySmarter!

Dot Maps

Dot maps, also called dot density maps, are great for showing density in an area. A single dot is assigned a value by the creator of the map. More dots in an area indicates greater numbers, while fewer dots indicate more sparsity.

Fig. 2 - This dot map shows the density of Malaria cases throughout Africa

Proportional Symbols Maps

A proportional symbols map, sometimes called a graduated symbols map, uses symbols (usually circles) of various sizes to show proportionality in a population statistic over space. Larger circles typically indicate greater numbers, while smaller circles indicate smaller numbers.

Fig. 3 - In a proportional symbols map, a circle is used to show proportional variations in space

The circles used on a proportional symbols map can also double as pie charts. This can be very useful when comparing multiple categories is a single area. For example, a proportional symbols map can use pie charts to display what percent of each US state voted for each candidate in a presidential election; the larger the pie chart, the greater the number of voters.

Flow Map

A flow map shows the flow of something—people, goods, or something else—from one area to another. Flow maps can be very useful for visualizing trade patterns, migration patterns, or military movements.

Fig. 5 - This 1864 map shows the flow of wine exports from France to the rest of the world

On some flow maps, you may find that thicker flow lines indicate a higher volume of flow. However, many flow maps are designed only to show the flow (and its direction) itself rather than both flow and volume.

Other Types of Thematic Maps

A cartogram manipulates the size of physical locations to demonstrate proportion. For example, a cartogram about which continent has the most kangaroos would be artificially manipulated to show Australia as the largest landmass.

A dasymetric map is, more or less, an advanced choropleth map. It uses colors to demonstrate comparative differences in a statistic but gets rid of most political boundaries to more accurately reflect an actual distribution.

In physical geography, a chronochromatic map uses different colors to demonstrate different features of the environment, like soil type or climate type, while a contour map may be used to show elevation (or differences in precipitation).

Importance of Thematic Maps

When you want to know where people are living and what they believe, or the economic relationship between different political entities, or voting patterns over space, you can simply read about it, or you can see it visually displayed on a thematic map. Which would you prefer?

The process of taking geographic data and making them visually accessible is called geovisualization, and thematic maps are one aspect of that process. Thematic maps enable private citizens and businesses to quickly look at the distribution of a statistic over space, which allows them to share visual information and make educated decisions.

Taking data and displaying them over space can be particularly helpful for governments. Where are citizens living? What are their demographics? How are they voting? Which cities are growing? Where is food being grown? Seeing these questions answered visually over space can help governments determine where to increase the availability of public services, and how to best meet the needs of particular populations.