So ive taken one of my fav maps (Daytona Beach) for Zero Hour and was trying to make it larger for more build room, and add a river through the middle. Everything went fine until I realized I needed to resize the map. It will let me resize the actual terrain and everything, but I can't figure out how to expand the border. Can someone please help? Thanks in advance.

oh, that is not a difficult problem. there is a border tool which is easy to find in the toolbar left side. when it is activated you can simply stretch the border with your cursor ;)
the bottom-left corner of the boundary can not be moved but here you can create new bounderies.

Wow, I feel pretty dumb right now. I had even tried that before and it didn't work but I guess it just depends on where you click the border to make it move. Thanks for the guidance.

Well, that will only adjust the active border. You'll also need to adjust the main border. Press ctrl+F & you'll see impassable terrain along with a dark blue border that should be on the outside of the active border. That's the main border (To see the active border, click on View->Show Map Boundaries. You'll then see an orange border.)

Now click on File->Resize... In the new window you'll see the X & Y dimensions of your map. To make the the map bigger, just raise those numbers. The default anchor in the center square. This means that after clicking OK, the map will get bigger from all sides. Pressing the middle left square will add map to the right side or vise-versa. The top left corner will add map to to the bottom right corner & so on...
In short, if you want to just have the map bigger from all sides, then increase the X & Y dimensions & click okay. If you don't like how it turned out, then just undo it, (ctrl+Z) & try again.

This will most likely move your trigger & water areas. You'll need to move them back in place. Also, you'll no longer see the orange active border aligned with the dark blue which looks like this:



Then click on the top right corner of the orange border & drag it to be aligned with the dark blue one.

okay, I am doing what Yoshi said. I resized the texture and the blue line moved. But, the yellow line did not. How do I stretch the yellow line out to the blue line?

Reading the instructions, it seems that you need to use the border tool to move the orange border to match the new blue border.

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what does the border tool look like?

I'm sorry, 😞 I should reword that part of my post.

...You'll no longer see the orange active border aligned with the dark blue one. You'll need to use the Border Tool, which looks like this:

Click on the Border tool & then click on the top right corner of the orange border & drag it to be aligned with the dark blue one.