Afaik, they only require the tag to be within the first 5 tags (same as we do for #travelfeed) since tags after the fifth position are only indexed by Steem engine tribes and not by most frontends. Adding custom tags works like on other Steem frontends, just separate them with a comma (or a space)
Hmm, I was having trouble doing that unless I was using the wrong section of the post creator. I was in "topics" and I was pressing comma after steemitworldmap and it wasn't accepting it. Same thing when I was trying to type newzealand or australia as a tag in travelfeed.
I noticed when I started typing, there were suggestions which then populated when you clicked on them from the drop down list. Was I looking in the wrong place?
I'll be back to write some more travel blogs in the coming weeks so will see if I have the same issue again.