Floods Leave 186000 Homeless, Brazil

Actually determining and counting the number of homeless is very difficult in general due to their lifestyle habits. There are so-called "hidden homeless" out of sight of the normal population and perhaps staying on private property.
Various countries, states, and cities have come up with differing means and techniques to calculate an approximate count. For example, a one night "homeless census count", called a point-in-time (PIT) count, usually held in the early Winter, for the year, is a technique used by a number of American cities, especially Boston, Massachusetts. Los Angeles, California uses a mixed set of techniques for counting, including the PIT street count. In 2003, The United States Department of Housing and Urban Development (HUD) had begun requiring a PIT count in all "Continuum of Care" communities which required them to report the count of people, housing status, and geographic locations of individuals counted. Some communities will give sub-population information to the PIT, such as information on veterans, youth, and elderly individuals as done in Boston.