+
         +
                                             +
----------+--------------+------------------+------------  poverty line


  +     +         +         +                 +

                                                            +
      +    +          +

                                  +      +            +
                        +                                       +
     +       +
                                               +

  +              +        +      +
        +
                                                     +

    +           +        +           +


          +               +            +               +


   +             +                +                          +


 +                              +