@Fleshus
The Gimp File -> New menu does have pre-set A* sizes set to 300 ppi for printing. You can use the A3 template 3508 x 4960 pix in either portrait or landscape mode, or if you want to keep the top and bottom in portrait mode, rotate the image 90 deg. (the printer can also do this but you might be happier doing it yourself)
I might have something like this, a rotated image with a 50% Vertical Guide Image -> Guides -> New Guide by Percent.
That splits the A3 image into 2 x A4 images using Image -> Slice Using Guides.
If your printer supports borderless printing you can set the print dialogue like (1) but do not do it.
Even commercial printers require an outside "Bleed Margin" (typically 5 mm) and an inside "Safe Area" to allow for paper alignment and paper cutting.
Use the printer to set the margins, as (2) Change the printing resolution > 300 first then you can adjust margins. Make a note of the settings for the second print. That should give sufficient "wriggle room" for paper not going through straight, paper feed needing bottom margin.....
The Gimp File -> New menu does have pre-set A* sizes set to 300 ppi for printing. You can use the A3 template 3508 x 4960 pix in either portrait or landscape mode, or if you want to keep the top and bottom in portrait mode, rotate the image 90 deg. (the printer can also do this but you might be happier doing it yourself)
I might have something like this, a rotated image with a 50% Vertical Guide Image -> Guides -> New Guide by Percent.
That splits the A3 image into 2 x A4 images using Image -> Slice Using Guides.
If your printer supports borderless printing you can set the print dialogue like (1) but do not do it.
Even commercial printers require an outside "Bleed Margin" (typically 5 mm) and an inside "Safe Area" to allow for paper alignment and paper cutting.
Use the printer to set the margins, as (2) Change the printing resolution > 300 first then you can adjust margins. Make a note of the settings for the second print. That should give sufficient "wriggle room" for paper not going through straight, paper feed needing bottom margin.....