Produce the prism map. The MIDPOINTS= option specifies the response levels for the map. The CDEFAULT= option sets the color of map areas that have missing data.

proc gmap data=sashelp.demographics(where=(cont=94))
          map=maps.africa density=low all;
   id id;
   format adultliteracypct percentn7.2;
   prism adultliteracypct / midpoints=10 to 90 by 20
                            cdefault=yellow;
run;
quit;