Megacities and Earthquake Risk

Read more about this map:
Paper in the Journal of Maps: Gridded cartograms as a method for visualising earthquake risk at the global scale

The following map is a modified version of the earthquake vulnerability map published on this website last month (see that page for more details on the underlying earthquake map). The map itself does not show much new information, but includes an aditional layer containing the largest cities of the world, the so-called megacities (depending on the definition, these are cities with a population of more than 5, 8 or 10 million). The circles reflect the category in which each city belongs (based on 2015 estimations by the UN), and they are placed on the location of the city related to the total population distribution. As the map is resized according to the population (equal-population projection), the map also help to understand the setting of each city within the global population density, explaining why the artificial boundaries of a city do not always tell the full story of the urban population structure within a region. In some areas, such as Hong Kong and Guangzhou in the Pearl River Delta, cities are just one of several centres in a highly urbanised region – an urban sprawl – while other megacities like Mexico City or Moscow are in a more solitary location (although even here the extent of the populated area goes beyond the urban boundaries, and certainly the population is far from solitude). Without the city labels the map already showed the relation between human settlements and earthquake risk. The following map now allows to better understand the underlying geography if one is not so familiar with that kind of map transformation.
On a more technical note, the following map feature also includes another jQuery feature (I experimented with the image slider applied to maps on the earth at night map): This map uses the Zoomy Plugin to reveal a more detailed version of the map using an interactive magnifier. Click on the map map to enable the magnifier and see more detail (or if you don’t like that, click here for the usual large version of the map).

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People at Risk: Visualising Global Earthquake Intensity

Read more about this map:
Paper in the Journal of Maps: Gridded cartograms as a method for visualising earthquake risk at the global scale
University of Sheffield Press Release
German-language news article: Weltkarte zeigt Menschen in Erdbebengefahr

Besides all the disturbing images in media, the devastating Japan earthquake has already been intensively documented in the world of mapping, ranging from USGS’s geophysical maps, ESRI’s Social Media mashup, and media features such as the excellent New York Times features (see here and here). More online map and imagery resources have been compiled by the editors of Directions Magazine (see here). Similar responses could already be observed during the Christchurch earthquake, which demonstrates, how fast such information is released and processed nowadays.
The following map shows a more general approach of mapping the risk of earthquakes. It is a visualisation of all major earthquakes that have been complied in the Global Significant Earthquake Database. The database created by NOAA’s National Geophysical Data Centercontains information on destructive earthquakes from 2150 B.C. to the present that meet at least one of the following criteria: Moderate damage (approximately $1 million or more), 10 or more deaths, Magnitude 7.5 or greater, Modified Mercalli Intensity X or greater, or the earthquake generated a tsunami“.
Following an approach of spatial-analyst.net, a kernel density has been calculated from these records to visualise the areas most at risk of earthquakes during that time period. In a last step, I have transformed the world earthquake intensity map (see map inset) using a density equalising cartogram algorithm applied to a population grid. Simply said, the resulting map gives each person living on earth the same amount of space while also preserving the geographical reference. This map allows to understand the earthquake intensity in relation to today’s population distribution, and thus gives an idea of where most people are of risk related to seismic activity (there is an updated version of this map showing labels for the world’s largest cities here: Megacities and Earthquake Risk).

Global Earthquake Intensity Map visualised on a gridded population cartogram.
(click for larger map)

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