i have the new 3ds so i dont know i it will be different, but yeah. i have seen some people posting pictures of their town maps and i really dont know how they do it.
To post a picture of your town map, you can go on Miiverse and it'll let you post pics of either the top or bottom screen. Choose the lower one and post it.
An alternative way is to go demolish a PWP and it'll show you your town map, and you can screenshot it with the method above or with the L and R buttons (but I am not sure of the new 3ds?).