Installing OpenCities Map requires a minimum of 12GB free disk space on your C:\ drive to download the package cache, otherwise known as the installation files. This is true even if you're installing on another drive such as your D:\ drive.
By default the location of the package cache is defined by the environment variable TEMP which is typically set to %USERPROFILE%\AppData\Local\Temp.
A quick workaround is to temporarily redirect the variable to another drive.
However, a solution that does not require editing your environment variables, is to redirect the package cache during the installation process.
To do that, run the installer exe with the following command line argument: IsPackageCacheButtonAvailable=1
Example: msa10020018en_updt2.exe IsPackageCacheButtonAvailable=1
Doing so will provide the installer dialog with an option button to redirect the cache location:
For more information, please refer to Redirecting the Package Cache