The original post is [here](https://forum.generic-mapping-tools.org/t/pen-style-not-work-for-map-grid-pen/5656). ``` gmt basemap -Rd -JQ5i -Bafg --MAP_GRID_PEN=4p,black,dotted -png test1 gmt basemap -Rd -JQ5i -Bafg --MAP_GRID_PEN=4p,black -png test2 ``` The first line gives:  The second line gives:  **System information** * Operating system: macos * GMT version (`gmt --version`): gmt 6.5