@JMarcell where did you get the original picture from?
09:18
You could of course scale it to something like 1024x1024, but it's better to find the source and check if it's available in a higher resolution, looks better ingame
@deen due to copying-mapres-from-other-maps several ones have the mapres in wrong reso as it was for sure saved by downloading forum's image thumbnail (thumbnail size is exactly 600x600px) in the first place(edited)