How about making a separate location like a small island?
What would the small island have on it?
But I didn't like the idea of making a entire map only for bridges, what about putting others stuffs?
The map has more than just bridges in it. There's tall grass for wild encounters, and still water for surfing/reflections/fishing/encounters. The tall grass also helps with showing off roaming Pokémon. And, if nothing else, it shows how to make a pretty map.
My design ethos is to make a small region, each part of which showcases a different feature. If you want to know how to make any kind of bridge, go here. If you want to know what you can do with an ice cave, all the possible puzzles are here. There will be warps to each area from the Nexus map. I think connecting them together is better than having isolated and/or cluttered maps, because it adds to the feel of the region and it also demonstrates a lot of map connections at the same time (i.e. so they don't need their own example maps).
Of course, most maps have multiple features in them. Perhaps the bridge map and other routes aren't the best examples of this, but certainly the towns have many different buildings (the large southern city contains a Poké Center, department store with elevator/stairs/marts/vending machines, Game Corner, Gym, fossil reviver and Move Tutor-type NPCs).
I spent a while coming up with the layout of the region, and I came up with a fairly decent distribution of features. Said features are all listed in my "To Do" file.