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What is a Choropleth Map and How To Create One

By Daleska Pedriquez, May 17, 2022

choropleth map

For organizations that need to report metrics like consumer demographics, sales performance, or population density across market segments, one of the biggest challenges is how to illustrate the data in a way that their intended audience will understand. 

Choropleth maps are among the most popular and effective ways of doing this. 

Let’s explore more about this solution and learn how you can create a choropleth map easily using Venngage’s Choropleth Map Templates.

 

Click to jump ahead:

What is a choropleth map?

A choropleth map is a thematic map that is used to represent statistical data using the color mapping symbology technique. 

It displays enumeration units, or divided geographical areas or regions that are colored, shaded or patterned in relation to a data variable. To show variation or patterns across the displayed location, choropleth maps provide a way to visualize values over a geographical area.

choropleth map
 

Readers can easily understand how a business’s market base has grown in the course of three years with a color-coded map like this.

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What is a choropleth map used for?

Choropleth maps are useful when the data you want to convey are:

  1. attached to enumeration units like cities, counties and countries, 
  2. standardized to show rates or ratios, and 
  3. in a continuous statistical surface, meaning measurable values occur everywhere within the area of study and not just at specific locations. 

This thematic map visualizes the amount of money each American state (enumeration units, within a continuous statistical surface) spends on health care in relation to the country’s GDP (standardized data). 

choropleth map
 

It’s important to note that raw data isn’t recommended for choropleth maps

This is because choropleth maps are comparative by nature. They’re commonly used to compare relative data and highlight their differences across geographic locations. 

For instance, the population of each city (raw) versus the population of each city in relation to its size (standardized). The former merely states the information while the latter provides comparisons between the data to illustrate the differences in the cities’ densities.

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How to read a choropleth map

A choropleth map is one of the most common thematic maps in use as it’s really easy to read and understand. If you are one of the few people who have little to no idea of how to read a choropleth map, let us walk you through.

To read a choropleth map, you have to read the instructions first as well as the color key or legend to understand what the shading or the pattern means. Next, look for the regions with the largest value shades, then look for the lighter colors to see the low values. Watch out for any significant regional patterns. You might come across neighboring areas that appear very similar or very different.

choropleth map
 

It’s easy to identify how the population in a country has declined because the data is accurately and visually displayed on this map. You can create more informative choropleth maps such as this using Venngage.

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What are the different choropleth map data classification methods?

Data classification arranges the data you include in your choropleth map with boundaries to separate each class from one another. The following are the different data classifications:

Natural break classification

Natural breaks is the default classification available for choropleth maps. Here, classes are based on natural groupings inherent in the data. This classification method should not be used to compare maps created with different data but only when you want to emphasize the natural groupings in your data.

choropleth map
 

This classed choropleth map presents information classified according to geographic regions. The data’s natural groupings are highlighted by their colors and legend. 

Equal interval classification

The equal interval classification method divides the range of attribute values into equal-sized sub-ranges. It emphasizes the amount of an attribute relative to other values and is commonly used for data that has familiar ranges.

choropleth map
 

A simple yet appealing classed choropleth map like this presents the percentage of adults with a bachelor’s degree or higher per state in equal intervals. Its matching color scheme, shapes, and fonts can be customized to best represent your data.

Quantile classification

The quantile classification method divides the attributes into binds with equal numbers of features. For example, a map that illustrates the rates of population growth of all 50 American states (attributes) might be divided into five quantiles or sub-groups with 10 states each (binds with equal numbers of features). Each quantile will be represented by one color on the map. 

The trouble with this method, however, is that it can complicate the look of your choropleth map as it can place similar values in different classes. 

For instance, in the earlier mentioned example, the rates of population growth might be divided based on the data’s chronological order (i.e. highest to lowest) versus the states’ geographic arrangement. In this case, the quantile colors will be scattered on the map instead of organized per area. 

This is why this method is better used on data that is relatively uniform. However, it can also be used as a method of visual ranking.

Standard deviation classification

The standard deviation classification method illustrates how much the data per geographic location deviates or differs from an average value. 

This method works best on datasets that are normally distributed and for analyses in which the mean, or the distance from the mean, is crucial. 

For example, a map that wishes to show how much Americans in every state spend on groceries compared to a national average amount per year.

Unclassed classification

The unclassed classification method is used when numeric data is displayed on a continuous scale, rather than in discrete classes. When you want to see gradual changes in your data, you can do so using this method.

Here’s an example of an unclassed choropleth map:

choropleth map
 

This map illustrates the average price of gas per American state through color codes and a scale that contextualizes the different shades. 

Manual classification

From the name itself, a manual classification method means that you manually add class breaks that are appropriate for your data. 

It should be used when there are known ranges that must be applied to your information, such as when you want to create a series of choropleth maps with the same classes or sub-groups to show their relation to one another.

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How to create choropleth maps online for free with Venngage

1. Create a free Venngage account

choropleth map

2. Choose a choropleth map template that fits your purpose

choropleth map

Use the data classification methods mentioned above to choose your map template. 

You should also think about the color ramp of your map: sequential (changing color gradient), diverging (gradual change of colors) or categorical or qualitative (color combinations).

choropleth map
 

This comparative map makes use of a categorical or qualitative color combination, using different shades of black and grey to effectively illustrate the differences between the data presented. 

3. Edit the data and text as you need

To edit, simply double click the map. A map editor pane will appear in which you can copy and paste the data in or import your data using a .csv file:

choropleth map

When designing a choropleth map, one good rule of thumb is to use the smallest unit for the data or, in other words, give preference to units such as counties instead of states, our countries instead of continents. This will help you give your readers a refined image of the information.

4. Customize your thematic map

To edit the color of the map, you can double click the map and choose “Settings” in the map editor pane. Here you can edit the colors of the two extremes, the color of the map when hovered over, etc.

choropleth map

5. Download your finished product or share it directly with your team.

After ensuring a perfect data visualization of the information you want to convey, share your design directly using a share link.

You can also upgrade your account to download your map in multiple formats (PNG, PNG HD, PDF, Interactive PDF, PowerPoint (to use with your slides) or HTML).

choropleth map

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You don’t need to be a data analyst or graphic designer to create choropleth maps

Choropleth maps are an easy and effective data visualization method to illustrate different values across geographic regions. Your audience also doesn’t need to be experienced map readers to make use of choropleth maps.

It’s easy to start creating choropleth maps using Venngage templates. Simply sign up for a free account and give our drag-and-drop editor a test drive! 

 
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