Tea Party Express Tax Day Rally on the National Mall, April 15th, 2010
This photograph of the Tea Party Express Tax Day Rally in 2010 is an excellent example of a classic crowd count. The aerial balloon image clearly shows a good view of the entire crowd gathered at the event. For the analysis of this event, DDIS used a traditional two-dimensional overlay grid. DDIS chose a 2D overlay strategy due to the size of the crowd, which allowed it to be counted entirely by hand. The yellow dots represent each person as they were hand-tallied using a mechanical counter. Small squares divide up discrete clusters of people while larger color-coded grids are used in less dense open areas.