Please look at the last screenshot. It explains how some Pokestops can be really close together. Plus there can be sponsored locations, and some really old ones could be breaking the current rules.
Forum rules do not allow me to link to a third party tool. It shows the cells as an overlay on the web submit nomination map form. It was created for the Wayfarer Discussion Discord. I am allowed to give the link to that: Wayfarer Discussion 5.29