The official Caesar 3 map editor is installed using an installer that was created during the Windows 98/2000 era. Later versions of Windows started having issues with this installer that resulted in the installer either not working or requiring compatibility settings.
This download works around that problem by providing the map editor files that are installed by the official installer in an archive. Now installing the map editor requires simply extracting an archive.
To install, simply extract the contents of this archive to the location you installed Caesar 3. If you are asked to overwrite any files, choose yes to overwrite them.