When displaying data, it is important to do so in a way that is as clear and as accurate as possible. This is particularly important when presenting data to an audience that may not be experts in that field. One of the most popular and effective ways of doing this is by using a choropleth map.
Choropleth maps are some of the most commonly used types of visual aids today. They use color to display data as shaded points, lines, and areas. A common example is the use of choropleth maps to show census data. The data is displayed as a map of shaded areas, each area using a different color or shade to denote a data point. They are useful tools as data is often collect as enumerated units. Choropleth maps help show these units visually, therefore making the data easier to understand for the layperson.
The big advantage of using choropleth maps is that they are able to express large amounts of collected data in a succinct, visual way. For example, population density is best expressed through choropleth maps. The combination of space and population density can easily be mapped onto a visual aid to help show how the data relates to the reality of the land type.
Some big advantages of using choropleth maps:
There is a drawback to displaying data in this way, however. Due to pre-existing boundaries, it can limit its ability to represent data realistically. This is because it does not allow for detailed fluctuations in the statistics to be shown.
It is important to remember that all maps are just one version of the reality they represent. They are not objective. They are dependent on many decisions about what is shown when they are being drawn.
It is important to choose the most effective color progressions to use when making your choropleth map. Always consider the data you want to represent, and think about how best to display it visually, using color.
Sometimes, cartographers use single-hue themes. This means that one color is used for the entire data set. The different data points are shown through a fading from dark to light, often including black and white at both ends of the spectrum. Dark usually represents the largest number, while white represents the smallest.
As mentioned earlier, choropleth maps often handle numeric data. This means that the data must be standardized as opposed to raw. They are sorted into two types: classed and unclassed.
The most common usage of choropleth maps is in visualizing population data. For example, employment rates and population densities.
They are extremely effective at showing the contrast between different pieces of data and making the impact more pronounced, especially for non-experts. If the data you are representing does not include regional patterns that would benefit from this type of visualization, then it may be worth considering an alternative.
The main use of choropleth maps is to show a more overall view of a collection of data — the bigger picture of what the data and research represent. They are not as good at showing detailed results, as they do not account for small variations in numeric data. Intervals between colors may not line up directly with those in your numeric data. By their very nature, they generalize.
We have linked two great examples of choropleth maps below to show how they can be used to great effect.
Creating your own choropleth map can be tricky at first. Luckily, there are many useful tools available that can make the process much simpler.
MapSVG allows the user to display content as a vector, image, or Google Maps. It is a commonly used plugin to make choropleth maps with and includes options to use filters and searches as well.
You can convert your numbers to colors on the map. In this way you can show statistical information and visualize your data.
It actually does more than this. You can create objects with custom fields: people, locations, events, real estate properties, or anything else. Import large data sets from a CSV file. Use a built-in template and CSS editors to set up the look of your content on the front-end.
This is a great tool that lets you make choropleth maps quickly and easily. When an area’s value changes, it automatically changes your map and the associated gradients.
This is another great online tool that helps you to create choropleth maps by assisting you with the coding process, which in turn will allow the user to embed the maps wherever they wish.
This editor is built on the data visualizer d3.js. It allows anyone to make easy choropleth maps with the speed and simplicity of familiar software such as Excel.
Datawrapper helps you simply map your data onto choropleth maps. The resulting maps are responsive and dynamic.
This tool has a huge range of styles of choropleth maps for you to choose from. There are over 500 available! Each one is shareable over social media, presentations, and more.
This software offers more functionality than others. If you want to not only create maps but edit and customize them, then JSCharting is a good choice.
Another great choice if you need to create clear and simple visualizations of your data is Kartograph. Easy to use for novices.
But it’s doable:
This map from 1826 is the first known example of a choropleth map. It was prepared by Charles Dupin (1784-1873). This map of France, in black and white, shows the number of inhabitants per department that had enjoyed a basic education.
An interactive choropleth map that uses different shades of red to show the sales of cigarettes in Europe by country.
A green-shaded choropleth map with data of the 2011 census. It shows the percentage of Australians that consider themselves Church of England.
An example of a colorful interactive choropleth map. Hovering over the map of the U.S. shows the population density of a state.
Choropleth map example of how COVID-19 spread in China. The data shown is as of February 24, 2020.
A choropleth of the percentage of urbanization by country in 1960.
The map above tells an interesting story. It shows the population change over 2014-2015 in the US. At a glance, it shows specific areas where the population is growing. These areas include the coasts, the North Dakota oil fields, and the Sun Belt.
This bivariate choropleth links two variables in one chart. It shows the percentage of people that voted for Donald Trump against their Medicaid coverage. It led to the conclusion that Trump is meanest to his own voters.
A choropleth map example showing the rate of excessive drinking by county. The shades of blue give an idea of the areas with high excessive drinking rates, such as Wisconsin. It also visualizes the parts of the US where drinking habits are less severe, like Utah.
The data in this choropleth is the population per county in Great Brittain and Ireland. It is shown as an average per county. So, it is good to keep in mind that this is an approximation of the density.
Visualization of urban displacement in the San Francisco Bay area.
ggplot2 is a popular tool for making simple choropleth maps. This post shows how to load geographical data, link with a numeric variable, and render it as a choropleth map. Another tool is plotly. This method makes a map interactive.
This choropleth chart shows the level of unemployment in the U.S. at the county level.
A single color scheme is used in this map. The population of Hispanics in the U.S. by state is shown using lighter and darker hues.
The subject of this map is the ratio between males and females for the 50 American states and Puerto Rico. Based on the 2000 census, the values are displayed as the number of males per 100 females.
An example of a bivariate choropleth map. A bivariate map is an efficient method to display two variables and their interaction. It makes the data and their relationship easy to understand. A bivariate map is also composed of a color code. Where a univariate choropleth uses only one series of colors, the bivariate map uses two series of colors. The combination of the two-color series shows the relation between the two variables.
This chart visualizes the world’s population density per country. A darker color corresponds with a higher population density.
The average number of children born alive to a woman during her lifetime. The factor that is considered is the fertility rate by age per year. The study assumes survival through the childbearing years.
A choropleth map example of the number of confirmed Corona cases per 100,000 inhabitants as of April 2, 2020. The data is split up by county. The shade of blue is related to the number of cases and the legend at the bottom shows the ranges by shade.
The seats in the House of representatives were reassigned based on the 2000 census. This map shows the gain and loss of seats. It is a variation of the choropleth map. The color scheme is used to show loss (red) or gain (blue). The number of seats in displayed by adding a number to those states that suffered a change. The states that did not see a change are assigned a grey color and no number is added.
Another example of a bivariate thematic map. The color scale is used to express the minority population. A dot of varying size represents the average family size among the minority population.
In this choropleth map, the New York City area is divided by ZIP code. The data represented is the average income for each ZIP code area. The darker the color the higher the income.
A graph reporting the number of Coronacases worldwide per country. The data is based on the information available from CNBC on March 17, 2020.
An interactive map showing the voter turnout in Europe by country. Two scales are used. Green shades are for countries where turnout was above the European average. Red is used for countries where less turned out at the last elections than the EU28 average. Just for comparison, at the last US elections in 2016, 61.4% of the electorate voted.
Map with a theme the percentage of adults ages 20 – 24 in the United States. A higher color saturation means a higher number.
This map shows Australia’s population organized by state.
A bivariate map combining population density data and change in population density over 1990-2000. For the population density, lighter and darker colors are used. To indicate the population change intervals a series of colors is used.
Percentage of Catholics in Ireland and Northern Ireland according to a 2011 census.
A choropleth showing the friendliness of the world by country. The additional information presents Iceland as the most welcoming country in the world.
The countries in red are friendliest or most welcoming. In blue the twenty least friendly countries are shown. By the way, The UK finished 55th and the US ended 102nd.
There is a reason that choropleth maps are already so widely used. They display data in a visual way, that makes the meaning and consequences of that data clear for all to see — including non-experts.
It is important to remember the failings of these maps, however. By the very nature of their design, they cannot show nuanced differences in numeric data. They generalize results for an overview rather than an in-depth look at the results.
However, if this is kept under consideration, they can be utilized to great effect. As with everything, it is important to consider what exactly your data is, as well as what it is attempting to show. This will ultimately help you decide whether or not using a choropleth map is the right way to go.
If you liked this article about choropleth maps, you should also check out this article with map illustration examples.
We also wrote about a few related subjects like the map elements, map vector, what is a vector map, interactive maps, how to make a choropleth map, thematic map examples, statistical maps, and all the types of maps out there.
I take it you like maps as well so make sure to check out MapSVG, a great WordPress maps plugin you should check out.