Crowd density is field-measured by visual estimation of people per square metre.
Evidence
The research assistants were trained to use the industry standard measure of crowd density (e.g., Still, 2014), which is to estimate from sight the number of people per square metre (ppm2) around each participant. — John Drury, The role of social identity processes…, 149
Categorization
- corroborated: 5 independent passages support this claim — John Drury, The role of social identity processes…, 149