I want to display the map only on demand (in order to minimize load time), means that any link, for example, "Show map", should display the map in the specified div. what should I do?
Just use the 'to_gmaps4rails' method described here: https://github.com/apneadiving/Google-Maps-for-Rails/wiki/Methods
Basically, do:
<%=raw assets_hash.to_gmaps4rails(true) %>
This only displays the js needed to display your assets.
So, enable gmaps4rails.js and .css (if necessary), and the div to place the map.