Here's my methodology for counting the #PeoplesClimate march in London.
My aim was to provide an auditable estimate of the number of people participating in the protest.
This is a personal project and as such the findings are not endorsed by my employer.
I set up a camera in a fixed position on the footbridge by Embankment station, overlooking the route of the march.
I took pairs of photographs, spaced roughly 30 seconds apart.