The Graduated Colour Map: A Minefield for Armchair Cartographers

Do not use choropleths for your COVID-19 counts, ever!

In a hilarious contribution to Medium, Dr. Noah Haber et al. issued a call to “Flatten the Curve of Armchair Epidemiology“. They analyze the transmission of “well-intended partial truths” about COVID-19 and caution of hidden “viral reservoirs throughout the internet”. To flatten this curve, they recommend fact-checking before posting and go as far as endorsing social-media distancing measures. As with general COVID-19 tips based on armchair epidemiology, misinformation can also be spread through the numerous COVID-19 maps that are widely circulating through the Web. In this article I want to focus on one particular instance of armchair cartography: wrongly mapping COVID-19 count data using choropleth symbology.

Choropleths are great-looking maps, my favourite thematic map type! They use graduated colour schemes to fill areas (the spatial units of analysis) to represent the magnitude (usually in ranges) of data collected for, or aggregated to, these units. But they can be deceptive in many ways, one of which arises from using raw-count data without adjusting for the different sizes of the spatial units. The above gallery of cartographic failures shows a small selection of misleading choropleth maps of COVID-19 cases published by major government and news media Web sites as of March 26, 2020.

Representing raw-count variables using choropleth mapping is a mistake that is notoriously difficult to explain. In “Mapping coronavirus, responsibly“, Dr. Kenneth Field notes the need to normalize raw COVID-19 totals to account for different underlying population sizes of China’s provinces. But in a related debate on Twitter, Dr. Stephanie Tuerk, a Senior Data Visualization Engineer at Mathematica, pointedly asks: “Can you further articulate the problem with using a choropleth to display counts? What precisely will people misunderstand?” She also questions the recommendation to transform count data into normalized rates, if the goal is to map the original counts. Indeed, I tell my cartography students that normalizing their data (by area, total population, or another reference total) will create a new variable and they need to think about whether that’s what they actually want to visualize.

The best explanation that I have seen as to the actual reason for the misrepresentation of raw-count data through choropleth maps was written by GIS Consultant and former Harvard Lecturer Paul Cote under the heading “Effective Cartography – Mapping with Aggregated Statistics“. Using the schematic figures shown above, Paul underlines our cognitive ability to understand quantity from graphics that vary in one dimension (size), such as in proportional symbols, in contrast to how we read intensity from colour (lightness, value), such as on choropleth maps. It appears that we are wired to understand a choropleth map as a representation of an intensity (e.g. population density per sqkm, infection rate per one million people), not as a count, and therefore this map type does not fit with raw-count data.

The cartography textbook by Dr. Terry Slocum et al. (2009) proposes an additional explanation. They note that we read information from a choropleth map as the probability of encountering a phenomenon. For example, if we look at Google’s world map of COVID-19 cases, China’s 80,000 cases put it in the highest class (dark blue). We’d therefore expect to be exposed to many infected people if we were to travel around that country. Conversely, we’d expect to find fewer cases in Canada, since this country’s 4,000 cases are mapped two classes lower (medium blue). Assuming we run into comparable numbers of people given space-time constraints (but ignoring current travel restrictions!), this is a wrong conclusion since Canada’s COVID-19 infection rate of 103 cases per one million population is roughly twice as high as China’s 53 (March 26 data from

It is important to note that this issue does not automatically occur on every choropleth map or between any two spatial units on a given map. In fact, I had a hard time finding a suitable pair of provinces or countries, in which the relationship between raw counts was inverted compared to that between normalized data. Yet, the possibility of this issue is what makes the choropleth map a no-go for visualizing total counts.

The above example also highlights another serious issue of the choropleth technique: It maps each value homogenously across its entire spatial unit, while in reality many phenomena are unevenly distributed within the units. Infectious disease is a good example of a phenomenon that produces highly localized clusters (China’s city of Wuhan, Italy’s Lombardy region, Germany’s Heinsberg district), which are poorly represented on any choropleth map that uses data aggregated to larger spatial units. The coronavirus pandemic demonstrates that improper cartography is not just an academic concern but can have serious real life implications – on public attitudes and even on policy decisions!

Pandemic Panic vs. Democratic Freedoms

Why Germans are more concerned than most about a COVID-19 lockdown

I have never been a supporter of Germany’s conservative parties but their leader, Chancellor Dr. Angela Merkel, is making German politics great again, at least seen from across the Atlantic. In a rare, televised address to the nation on 18 March 2020, Dr. Merkel urges her “dear fellow citizens” to voluntarily practice the hygiene and distancing measures recommended by public health authorities. At the time, there were some 12,000 confirmed COVID-19 cases and 28 deaths in Germany.

Dr. Merkel’s speech can be seen as a last attempt to avoid enforcing stricter isolation rules. There is a unison of voices from politicians, epidemiologists, and the public calling for the “total shutdown” of society to stop the coronavirus spread, both in Germany and over here in Canada. Merkel however conveys a deeper understanding of the risks of social isolation. She characterizes COVID-19 as the greatest challenge faced by Germany since WWII – not in general terms, as was wrongly reported, but in terms of a challenge that requires every single person’s solidarity and commitment to flattening the curve. Merkel acknowledges the degree to which limitations on non-essential activities are already invading not just our personal lives but our understanding of a democratic society. She refers to her upbringing in totalitarian East Germany and the struggle to fight for the freedom of movement that is now effectively being withdrawn. She established that “such restrictions can only be justified if they are absolutely imperative” and “these should never be put in place lightly in a democracy and should only be temporary.”

Fast forward five days to March 22nd and approaching 25,000 COVID-19 infections and 100 deaths, Germany’s federal and provincial governments agreed on a contact ban, but still did not impose a general curfew. Citizens are free to leave their homes for any purpose as long as they keep among their co-habitants or stick around with no more than one other person. In a commentary entitled “The Other Danger“, Die Zeit journalist Christian Bangel acknowledges that Merkel did not take the easy route. He views her speech as a reminder of what is at stake, reminder to those who call for more drastic measures. Bangel, also born in East Germany, notes how many people who usually lament Germany’s culture-of-prohibitions (“Verbotskultur”), e.g. when it comes to taking climate change action, now call for lockdowns and celebrate the Bavarian premier for jumping the gun with a province-wide curfew. Bangel cautions against the collective-conformist effect of the coronavirus panic, when we forget the difficult balance of freedom and safety in our democracies. He asks what restrictions on civil liberties will be acceptable in the next crisis situation? Accepting such restrictions out of ease and convenience reminds me of how we willingly trade privacy for the convenience of digital services. Bangel concludes that in addition to fighting the virus we also need to fight against complacency and an attitude that views civil rights as a burden for public health and wellbeing.

Germany has learned from two totalitarian regimes in its not too distant past, and Dr. Angela Merkel, the Leader of the Free World according to some, set the tone for a thoughtful, measured pandemic response. Maybe that’s what you get with a conservative, female leader who boasts a doctoral degree in physical chemistry. Merkel shows great empathy when she thanks supermarket cashiers and warehouse employees for keeping things going (“den Laden am Laufen halten”, akin to the expression “the show must go on”) and is cited with the frustration over keeping families from enjoying the sunny spring weather if confined to their homes. In addition to the political dimension of the crisis, I expect that we will also see broader public health issues from a wide-spread sedentary life style under coronavirus lockdowns. Our mental health will be challenged to say the least. And the expected increase in domestic violence is a real danger, too. I therefore hope that other leaders will take a page from Dr. Merkel’s book and avoid full lockdowns or clearly limit them in duration, plus justify them in the context of democratic standards and civil liberties.

To be clear, I am not suggesting to take the coronavirus pandemic lightly or disregard public health guidelines, rules, and laws. I do argue to take a step back and not call for hasty political decisions in a panic. Some experts even recommend “social-media distancing” to “Flatten the Curve of Armchair Epidemiology“! Let’s consider the possible longterm impacts of our response and ensure that we as individual citizens can continue to monitor our authorities’ actions rather than be locked out of decision-making. But ultimately, a slowing of economic and social life under COVID-19 may not be such a bad thing, for nature and humans alike.

Geospatial Analysis for Pandemic Response

Why studying Applied Geography is more important than ever

Today was going to be Ryerson University’s Open House for prospective students, those already admitted for Fall 2020 as well as those considering a late application to our programs. The event was cancelled as a consequence of the distancing measures taken to slow the spread of the novel coronavirus. As undergraduate program director for the BA Honours in Geographic Analysis and past graduate program director for the MSA in Spatial Analysis, I would like to share some thoughts about why it is now particularly important to recruit bright students into Geography programs.

As you monitor the #COVID-19 news coverage, you can’t help but notice an abundance of maps and graphs. Many politicians and administrators refer to the importance of “the data” to make evidence-based decisions. The data in question are public health data – confirmed and suspected cases, recovered and deceased, tests completed, etc. – and as always, location information is a key component of these data. Geographic concepts such as distance, connectivity, clustering, and scale are at the very core of the issue, since the nature of an infectious disease such as COVID-19 is inherently spatial. But Geography is a meta discipline, its concepts apply across almost all areas of human activity. In addition to public health, it determines retail location decisions, financial transaction monitoring, environmental pollution and conservation efforts, crime pattern analysis, and transportation planning, to name only a very few examples.

Ryerson Today story from February 2018, outlining extensive career opportunities for Geography graduates

Geography programs across North America are struggling to recruit students because it is notoriously difficult to explain our subject matter compared to seemingly clear disciplines such as psychology, outline career opportunities compared to say business or law degrees, and show its visible impact compared to e.g. urban planning. Therefore please pardon me for using the coronavirus crisis to explain the importance of recruiting some of our best high school students into Geography programs. Canada needs these graduates to take on some of the most important analyst, planner, and decision-maker roles in our society!

Geography at Ryerson is deeply committed to offering programs of study and courses that are directly relevant to today’s community needs. In the BA in Geographic Analysis and, at an advanced level, the MSA in Spatial Analysis, we teach technical skills and critical thinking for data analysis, visualization, and interpretation. This winter 2020, students in my course GEO641 “GIS and Decision Support” first used professional geographic information systems (GIS) software to identify areas for possible urban expansion in the Toronto region within the constraints of the Ontario Growth Plan. We then moved on to create indices of neighbourhood wellbeing in Toronto and visualize them in Esri’s Operations Dashboard product, the tool used by Johns Hopkins University’s Center for Systems Science and Engineering for their now-famous coronavirus map. The final lab assignment in my course is a web map to explore the United Nations Human Development Index, another real-world example of using GIS to address some of humanity’s greatest challenges.

Esri Canada’s online interactive geospatial dashboard within their COVID-19 resource hub

Along the way, students learn about integrating disparate datasets, handling missing values, properly normalizing indicators, applying sound cartographic styles, and correctly interpreting the results. These are issues encountered in many of the “viral” visualizations of COVID-19, as discussed by Kenneth Field in “Mapping coronavirus, responsibly“. For example, my favourite Toronto newspaper, along with other news outlets and social media influencers, are still mapping global COVID counts using graduated colours (choropleth technique), which conveys false information about the spread of the virus and must not be used for decision-making. The world needs more geographers who are ideally positioned to tell stories behind the data and turn valid insights into proportionate action.

Some of the information collected for Esri Canada’s COVID-19 resource hub is sourced from another industry partner of Geography at Ryerson: Environics Analytics, a “leading data, analytics and marketing services company specializing in geo-demographic segmentation, site evaluation modeling and custom analytics” ( Environics Analytics provides $10,000 per year in scholarships to our students, attesting to the immense importance of geospatial technology training for their business and growing workforce.

Ryerson geographers working as junior and senior GIS analysts as well as undergraduate and graduate interns at BlueDot (as of 2016)

Another example of the connection between Geography and Public Health is BlueDot, a research and consulting firm founded at Toronto’s St. Michael’s Hospital, just down the street from Ryerson. BlueDot was widely credited in the media for being one of the first organizations to warn of the novel coronavirus epidemic in China and the threat of its global spread. BlueDot conducts infectious disease modeling and monitoring using big geospatial data, geographic information systems, and artificial intelligence. About 20% of BlueDot’s staff as of early 2020 are Ryerson Geography graduates, primarily working in data engineering and software development, and BlueDot is currently seeking to expand these teams.

A university education in Geography goes well beyond the conceptual and technical competencies needed to analyze and interpret geospatial data in the workplace. Geographers are also equipped with critical thinking skills required to solve complex problems and understand the limitations of analytics. In the context of COVID-19, I notice concerning reports about the extent to which individuals are tracked using cellphone data (e.g. Germany, Israel), the use of drones for policing curfews (e.g. Spain), and general calls for drastic social isolation measures that could become politically dangerous and detrimental to our mental and physical health. Geographers know what is technically possible but also what is at stake, and are therefore among the few professionals that I would trust to balance decisive crisis response with concerns about its long-term implications. We need many more geographers to make the world a better place!