Chicago is bracing for a gigantic crowd this week in Grant Park, the city’s iconic front yard, where Senator Barack Obama has chosen to spend election night. As many as 70,000 people are expected to attend an event for local supporters. All available tickets were swept up days ago, and thousands of people have applied to be on a waiting list. Thousands more — maybe as many as a million people, Mayor Richard M. Daley has proudly suggested — are expected to pile into the downtown parkland and sidewalks and streets surrounding Mr. Obama’s official celebration. “This could be...