Thread by @spatialanalysis

John Snow's map of cholera looked as dull as (cholera filled) dishwater compared to his competitors...
His brilliance was a solid data collection & then a simple map presenting what he knew.
Each death marked in black and white.
Here's a lesson for COVID-19 dataviz...
1/11

Of course, cholera remains a global issue killing tens of thousands a year.
Here's an early map showing its spread from India to Britain...we've seen so many recent versions of this with COVID-19.

As it arrived in Britain towns and cities were hardest hit...here's the extent of the epidemic in 1849.

Still no sign of Snow's map at this point...but it was getting serious in London...

People wanted answers so William Farr stepped up. He was a rigorous statistician & excellent data visualiser. His (and the prevailing) theory was that cholera was spread by bad smells "miasma". London was a smelly place and outbreaks peaked with hot weather when it was smelliest.

Farr's charts make a particularly beautiful case for the miasma theory...

And others made scary maps showing the "cholera mist" as it spread across London...

So Snow had his work cut out...he pounded the streets getting detailed on the ground data - not just headline figures for cities. The black bars on his map show a death from cholera. I think it has a humanity that Farr's visualisations lack...

Of course, they were an essential rebuke to the miasma theory and enabled the attention to turn to London's water supply. It turned out that certain suppliers were responsible for higher deaths than others...

...and also looking to the geology of London in later years.

These maps come from the brilliant Wellcome Collection: wellcomecollection.org/works/
And I wrote a similar threat with full sources back in 2018 spatial.ly/2019/03/mappin… /ends.