Each line is one part of the federal income security budget. The top line gathers the other income security programs, which grew from about $26 billion in 1998 to a peak near $57 billion in 2011. Housing assistance through HUD is the second line, cash welfare through TANF the third, and the nutrition programs shown here the lowest.
All four rise into the Great Recession and then flatten or fall, which is what a safety net is supposed to do: spending grows automatically when more people qualify and shrinks as they stop qualifying. The last two years are budget estimates rather than outturns. The slider reads all four series at a chosen year; the values are read from the book's figure.