The number of participants define the categories

Cities that take part of Challenge Day are grouped according to the number of inhabitants, in seven categories:

• Category 1 – up to 9.999 inhabitants
• Category 2 – from 10.000 to 19.999 inhabitants
• Category 3 – from 20.000 to 49.999 inhabitants
• Category 4 – from 50.000 to 99.999 inhabitants
• Category 5 – from 100.000 to 249.999 inhabitants
• Category 6 – from 250.000 to 999.999 inhabitants
• Category 7 – over 1.000.000 to inhabitants

This criterion follows the official number of inhabitants of each city, according to local census.