Create annotate data set, REFLIB.CENTER, from MAPS.USCENTER. The annotate data set labels each state with a two-letter abbreviation. MAPS.USCENTER provides the x and y coordinates for the labels. FLAG, which is initially turned off, signals when external labeling is in effect. The labels are drawn after the map because the value of WHEN is a (after).
   length function $ 8;
   retain flag 0 xsys ysys '2' hsys '3' when 'a'
          style 'swiss';
   set maps.uscenter
       (where=(fipstate(state) ne 'DC')
       drop=long lat);