Note on construction of t109
t109  Approximate non-agricultural urban P 

   * 1) When t105<t102, t109=t105.
     2) When t102=0, figure t109 as t105/3.
     3) When t105>t102, calculate t105 as follows:

   When t105/t102>1.0 but <2, t109= (t102 + t106)/2 
           "      2.0   "  3    " = (  " + .95 t106)/2 
           "      3.0   "  4    " = (  " + .90   " )/2 
           "      4.0   "  5    " = (  " + .85   " )/2 
           "      5.0   "  6    " = (  " + .80   " )/2 
           "      6.0   "  7    " = (  " + .75   " )/2 
           "      7.0   "  8    " = (  " + .70   " )/2 
           "      8.0   "  9    " = (  " + .65   " )/2 
           "      9.0   " 10    " = (  " + .60   " )/2 
           "     10.0   " 11    " = (  " + .55   " )/2 
           "     11.0           " = (  " + .50   " )/2