At large events police are sometimes asked by the media how large the crowd the crowd was. Often police estimate how large crowd sizes will be for officer deployment and planning reasons. During the events we attempt to to determine crowd size; again to determine if staffing and planning were meeting our needs. I spent some time at the Christmas City parade last night and talked with staff about crowd size. One of the measurements we used was the amount of available parking downtown and in surrounding neighborhoods. It appeared all ramps and on-street parking was full with many people parking and walking a considerable distance. On a normal work day it is estimated the downtown population is just under 25,000 people. Considering normal ramp vacancies and street vacancies our staff estimated the parade crowd at over well over 35,000 people. However, as this article points out, these numbers are not scientific.
Check out this article on crowd sizes.
We ceased providing crowd numbers for some of the local rallies a couple of years ago due to the additional and unnecessary controversy it created.