Part of this is because the Overview tab counts homeless individuals whereas the People tab counts homeless households (i.e. a married couple with two minor children counts as one homeless "family" in the People tab and as four homeless "citizens" in the Overview tab), but there also appears to be an underlying issue with how the game counts people - you can often get two or three different figures for Tropico's total population by summing up the numbers in the population breakdown by age category, by wealth category, by educational level, and by employment statistics (be sure to include children and retirees from the age breakdown and criminals from "Special Citizens" as on most constitution settings Tropicans in these categories are not included in employment statistics), and these figures will usually differ from the total population listed at the top of the People tab or on the main game screen.