Map failure

So, I've seen this since I'm "map connecting" my maps

i.imgur.com/tBPSXWv.png
(You would have to copy/paste sorry :( )

If you look there is some black lines and I don't understand why it's doing this.

So if someone can tell me what I did wrong that would be great, thanks ^^

It's probably the well-known scaling issue with higher resolutions. Not with connecting the maps.

Hmm, what do you mean?

Are you playing on fullscreen? If so, that's the issue. There's a rounding issue with the scaling for bigger resolutions.

No, I'm just playing with the debug size.