Create a format for POP.POPFMT. defines the ranges of values for POP and labels the values.

proc format;
  value popfmt low-1000000="0-1"
               1000001-10000000="1-10"
               10000001-100000000="10-100"
               100000001-500000000="100-500"
               500000001-high="over 500";
run;