Dot Density
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Let’s try a different thematic map that will let us be a bit more specific.
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A dot density map uses a dot to represent a key feature or attribute.
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The cartographer decided that each dot on this map represents 100,000 people.
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So while the choropleth map showed the general population spread out over an entire country,
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this dot density map has more granularity and shows where within a country people live.
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More or less.
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We can see the coasts of Brazil have more dots -- and more people.
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But take a look at the Sahara or Siberia.
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No one lives exactly where those dots are!
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The cartographer also decided where to place each dot to summarize population data.
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But it’s a simplification that could mislead someone if they're not paying close attention
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like we are!
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A dot doesn’t necessarily mean 100,000 people live exactly there.
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Cartographers are always trying to make maps easily readable, but all the choices they
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make can influence accuracy.
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For example, if we changed how our dot density map is projected, or how the 3D Earth was
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flattened into 2D, the size and shape of the continents would shift, and so would the dots.
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We might accidentally imply some areas have a closer population density while others are
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more spread out.
Cartogram
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Our last thematic map for today is a cartogram map, which uses size to compare data -- like
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population density -- regardless of the actual space these regions take up on the Earth's
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surface.
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With this map, the really populous countries are giant, while ones with smaller populations
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are tiny.
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But it looks weird to us or at least me, because we're used to maps that tell us something
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about the physical space that countries and continents take up.
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India has a much bigger population, but in real life Australia is a muuuuch larger country
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-- it’s about 7.7 million square kilometers while India is less than half the size with
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3.28 million square kilometers.
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Each of these thematic maps uses a different lens to tell the story of the world population.
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Different maps represent data in different ways.
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And the more information a geographer has, the better interpretations they can make about
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a particular story -- like human population.
Perception of Reality
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Of course, there are many, many more stories to tell, so there are many, many more maps.
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And by helping us visualize data across space, maps actually shape our perception of reality
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too!
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Alright, that sounds a bit melodramatic.
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But every map was made by a person making choices.
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And those choices (however thoughtful, or simple, or unintentionally biased) have an
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impact on how we imagine the world.
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Like, we’re so used to seeing north at the top of a map and south at the bottom.
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But why?
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Well, that's a choice made by a cartographer.
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Other cartographers tried something different with a Fuller projection that unfolds the
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Earth and ends up with a completely different orientation without distorting anything.
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This map doesn’t have Greenland at the very top of the map, like we might be used to.
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There’s more than one way to represent Earth.
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By thinking about what a map was supposed to be used for, we can spot these obvious
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or not-so-obvious choices made by cartographers.
Stick Charts
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For centuries humans have been using maps as navigational tools to help us understand
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our physical surroundings.
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Stick charts like these are made of fibers from coconuts and shells that were developed
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by mariners from the Marshall Islands.
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These charts weren’t used to navigate exactly the same way that we use maps today.
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They weren’t carried along in the boats, but studied and memorized to get a better
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idea of the islands, waves, winds, and currents in the Pacific Ocean.
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Stick charts were personal -- mariners had their own stick charts that they used to get
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back to places they’d visited.
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Kinda like my mental map to my favorite coffee shop.
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These charts were someone’s own perception of the space in their individual world.
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Maps can also be used politically, and the choices about where to draw borders on a map
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are giving spaces a national identity.
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For example, there's a dispute over territory in Antarctica and some nearby islands that’s
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currently on pause thanks to a 1959 treaty.
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Originally the 12 countries whose scientists had been conducting research on the continent
List any questions you think of
1. How does a dot density map differ from a choropleth map?
2. How does a cartogram map represent data?
3. How do maps shape our perception of reality?
4. What are stick charts and how were they used for navigation?
5. How can maps be used politically?
1. What is a dot density map?
2. How does a dot density map represent population data?
3. How do cartographers decide where to place each dot on a dot density map?
4. How can the choices made by cartographers impact the accuracy of a dot density map?
5. What is a cartogram map and how does it compare data?
6. How does a cartogram map represent population density?
7. What are some examples of other types of thematic maps?
8. How do maps shape our perception of reality?
9. Why do most maps show north at the top?
10. What are stick charts and how were they used for navigation?
11. In what ways can maps be used politically?
12. Can you give an example of a territorial dispute that is reflected on a map?