Man, I'm having this same problem. Along with about two dozen others. I've found that its just tough luck if your not a modder. All my (very) limited knowledge of modding comes directly from my futile attempts to address concerns that I believe we all feel should be simple interfaces in such a popular franchise such as civilization.
I've been trying in vain for about two months to get my custom maps to flood. I've tried using the Ynmap converter, to attempting (again in vain) to convert my custom maps into .lua files. I've tried writing to 2K support. I don't understand why Firaxis couldn't have made a simple method to import custom maps or allow their new features to be enjoyed on them. If anyone out there reading this has a non-modder, simple to understand solution to any of these issues, I and a bunch of others would be grateful