northwest of the yellow line at the top left corner of the map -- the "bulge" north of the Han river -- is the part of NK that is closes to seoul airport. it's a well-fortified hilly area. the map includes the range of the M-1978 170mm self-propelled gun, but not the more advanced M-1998 170mm SPG or the 240mm MLRS (multiple-launch rocket system). estimates of how many of these long-range artillery pieces NK have varies, but a total of 500 to 1,000 is a reasonable number.