I've created a map system for a game that runs on the principle of drawing the picture of the map from tiles. There are many reasons for this which I won't go into here but if you really want to know then I'm sure you can find out how to contact me ;)
I have made the latest version live so you can see exactly where the problem lies and the source. The issue is the line between the top 2 tiles and the bottom 2 tiles, I can't figure out why it's gone like this and any help would be appreciated.
In the source is a marker called "stackoverflow", if you search for "stackoverflow" when viewing source then it should take you to the table in question.
I have also uploaded an image of the issue.
Thanks in advance for any help you can offer.