How does conversion work?

[Psychotronics]

I'm playing my first game, started as Han, now I'm Ming. I founded the religion of Confucianism and I'm trying to spread it, but the conversion mechanic isn't completely clear to me.
When I send my missionary to a city and spread my religion, it says "Urban Confucianism". I noticed there are two little circles containing the city's religion. Once I spread it, one of the circles changed to Confucianism, but I can't spread it anymore. Since it said "Urban Confucianism", I imagine there must be some rural settlement I can spread to but... which? I haven't noticed any indication of where to spread my religion other than the city center itself.

 

[Fat Bastard]

You have to spread it to urban and rural districts. The rural districts are things like farms, quarries, woodcutters etc.