It sound like you need a join table between the People and the Event tables. This would hold the individual's ID and the event's ID. You could then use that relationship to see which individulas were associated with each event or which events and individual was associated with. You should also be able to filter the events by city if that is a field in the Event table.
Rather than having multiple event or city fields in the People table for an individual that attends events in multiple cities, you have a small join table that maps between each person and each event they attended.
I wouldn't copy data from events to your individuals. If you then discover the need to modify information in the event record, those changes will not appear in the other records until you find and update each individual record linked to that event. As Mark as suggested, just use the link to the related event record to display the data.
Here is a demo file that just so happens to match events to contacts in the many to many relationship Mark has suggested. It's intended to illustrate methods for working with many to many relationships--not how to manage events and contacts specifically, but it may have some ideas you can use: http://www.4shared.com/file/dZ0bjclw/ManyToManywDemoWExtras.html
If you want to select a city and see a list of values specific to that city appear in the value list for anoather field, set up a conditional value list.
Here are some links on conditional value lists.
Forum Tutorial: Custom Value List?
Knowledgebase article: http://help.filemaker.com/app/answers/detail/a_id/5833/kw/conditional%20value%20list