An MPQ archive can be thought of as a zip or any other archive file. Inside are files that could be thought of as being arranged in some form of file structure.
There are 3 main MPQs that WC3 uses. These are the orignal RoC, orignal TFT and patch archives found at the install path of WC3. You can use an MPQ editor to extract game data files from them.
Among the data files in them are the campaign map files that are editable with the WorldEdit. The RoC and patch data files contain the orignal campaigns while the TFT and patch contain the expansion campaigns.
war3.mpq - Orignal RoC data
War3x.mpq - Orignal TFT data
War3Patch.mpq - Patch data (for both)
War3xlocal.mpq - Localized data of some form (language specific)
1. Get a MPQ editor.
2. Open the right data MPQ archive.
3. Extract Campaign maps.
4. Open and Edit in WorldEditor.