Is it possible to expand an existing map, example is china 04 in ZH, it I wanted to make more to mess with in terms of supplies or even more enemy bases to fight.

There is a resize option under File tab

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how do i expand the ..... playable border? the area box that indicates how much play space you have.

ah that - you can use rescue pilot mission as an example - go try open it on worldbuilder and see the scripts for yourself

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There are two options:

1. The border tool, it allows you to move the north and the east border but it might screw up the map

2. The resize tool (File -> Resize) adrianemapmaker was talking about, which can move all border sides but also might screw up the map :D

Map a backup before doing experiments.

If you can't get it to work, paint the new border position that you want with a texture and upload the map file here.

Ok so I was using the Generals USA mission 7 to try and do this, the yellow/orange border that defines how big the play area is.
I can move it east and west but not north and south.

Is it controlled by scripts or something?

I was hoping to add an area behind (to the right) of the abandoned Chinese base with oil derricks and refinery instead of the one that had no use in the city.

you can script what active border will be used ingame = as i said you can just look at the rescue pilot mission from vanilla generals and see the scripts for yourself - just try experimenting on that map other than any map

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