The Point-in-Time Count, or PIT Count, is an annual survey of homeless people in the United States conducted by local agencies called Continuums of Care (CoCs) on behalf of the United States Department of Housing and Urban Development (HUD).
[1] HUD uses the data from PIT counts to evaluate the effectiveness of local agencies' efforts to address homelessness and to determine funding amounts for them, and also compiles this data into the Annual Homeless Assessment Report, which is provided to Congress.
The unsheltered count is more difficult as it generally involves volunteers traveling to places where they expect people experiencing homelessness to be (under bridges, encampments, etc).
[6] The risk of undercounting can be greatly diminished through the increased utilization of Homelessness Management Information Systems (HMIS) to capture data from people experiencing homelessness who stay in emergency shelters, transitional housing, or safe haven projects.
Once compiled together, the data from both can be used to generate an accurate "by-name list" of everyone who is experiencing homelessness in a community at any given point-in-time.