Thematic Maps: Definition & Types

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  • 0:01 Thematic Maps
  • 0:42 Choropleth Mapping
  • 1:19 Isoline Maps
  • 1:59 Dot Density Map
  • 2:37 Flow-Line Maps
  • 3:11 Cartograms
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

Maps come in all shapes, sizes, and colors. In this lesson, we will review several examples of thematic maps and see how each can be used to analyze or disseminate data.

Thematic Maps

In the modern world of GPS and smartphones, many of us have forgotten how to appreciate a good old-fashioned map. Maps are awesome. They're full of information and provide such a specific and distinctive understanding of physical space and the people who live there. In fact, maps are amongst the primary ways that we categorize and analyze information about how people interact with and within physical space. Of particular use are thematic maps, those which are designed to illustrate a specific theme in relation to a geographic area. Whether it's trade patterns, or the spread of disease, or even the definitive ranking of people's favorite flavor of potato chips by state, thematic maps always have something fascinating to share.

Choropleth Mapping

Let's look at some of the common ways we create thematic maps. One frequently used system is choropleth mapping, in which statistical data is plotted over predefined geographic areas by coloring them in. For example, if I were to gather statistics on the frequency of bicycle use by state, I've got data that is sorted by a predefined geographical unit, in this case US states, so I could make a choropleth map. Generally, this is done by picking a color, say green, and having different shades represent different values. A state that frequently uses bicycles may be a solid, dark green, while a state that rarely bikes is a light, bright green. That would be a choropleth map.

Isoline Maps

Choropleth maps are fun, but that's not always the best way to map information. If you've got data that is not related to predefined geographic borders and instead focuses on continuity over distance, you might want to consider an isoline map. Isoline maps use continuous lines to indicate points of the same value. You've actually probably seen these before. If you've ever read a map where the landscape is represented as lines of elevation, that's an isoline map. Another common example can be found on the nightly news during the weather segment. When the weather map is divided into lines of pressure, often used to show storm systems, points of the same value are being connected as continuous lines, so it's an isoline map.

Dot Density Map

For another type of thematic mapping, let's turn to dot density mapping, in which dots are used to indicate the presence of a feature. Imagine a map of the United States, now place a dot on it showing where you are. That's a dot density map. You are the only data point on that map, showing us that you are unique. Now, place a dot on the map for every person in the United States of your same gender, or your education level, or your income, or your last name. The distributions of dots over space help researchers identify patterns, especially when you don't necessarily know what you're looking for. These commonly are used to map the spread of disease as a way to locate the source of the disease or areas of high infection.

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