coast line map - 海岸線のみ入った白地図をつくる　
  使うコマンド　　coast   basemap

sample map

bash スクリプト例
#  make coast line map Modern

# parameter setting
region=130/145/25/35                    # map region east/west/south/north
proj=M10                                        # map projection and scale
ticks=a5f1g5
frame=WSne+tbasemap       # boundary tick info and title
#
gmt begin coastbasemap
       gmt coast -R$region -J$proj -Di -Ggray -Wthin,black
       gmt basemap -B$ticks -B$frame -V
gmt end show



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