In Linux, if you set the environment variable GDK_SCALE to 2, then Grid Cartographer's rendering breaks completely. The Grid Cartographer application only occupies the lower left portion of the window and widget (the rest of which is blank), and the mouse hotspot is quite a ways below the mouse cursor. It looks to me like Grid Cartographer's calculations might be making some assumptions that stop being true after GDK_SCALE is set to 2.
Setting GDK_SCALE to 2 is a standard way of scaling up GTK3 widget for HiDPI (e.g. Retina) displays. As documented here:
https://wiki.archlinux.org/index.php/Hi ... TK.2B_3.29
I intend to run Grid Cartographer on 2015 13" retina MacBook Pro that boots into Linux, so there's at least one person that will be very happy if you fix this.
Thanks for reporting problems here.