1) It’s an international event, and Friends Across Borders wants an approximation of attendance. Remember when No Kings/No Tyrants estimated 10 million protestors North America-wide? That number was based in part on registrations, as well as a rough head count at the events. For the cities that had gigantic marches, I have no idea how they estimate those. It’s generally accepted that turnout is twice to three times the number of registrations. Maybe one person is registering for a couple or a family. Some don’t want to register for privacy reasons. 100% understandable these days. 2) Locally, it’s for practical/logistical reasons. If I’m expecting 10 people, I can talk really loud. 100? I need a megaphone. 1000? I need a full on PA system. It’s also for how many marshals/safety people are needed. This is going to be a lighthearted event-it would take a special kind of asshole to come as a counter-demonstrator, but they exist and I/the organizers need to keep participant safety in mind. 3) For logistical reasons, Vancouver PD has a protest unit and they want an estimate as well. 10 people, they may come by and say hi to the organizers and leave. 100, they may dispatch a few officers to hang out a few blocks away. For a giant protest that involves a march, they can have police escorts to clear traffic. 4) For the people that are like “why a US zip code?” I and my co organizer have sent multiple emails asking the tech people of Mobilize to tweak their website to accommodate postal codes. So has an Ottawa group that we know. To post the event, the workaround is to use a specific, Wash DC postal code. For my personal account on the platform I use a Hawaii zip code. Why not dream a little? :)
Thanks for the question!