Preset Map Nodes for Every Map

I am wondering how to include preset map nodes. For instance, every post on my site has a location (in my case restaurants). I want the location of every (in my case) bart station on the map when I make posts. So when users see the map of the restaurant (blue push pin), they could see the closest bart station (red push pins). It would be even better if they could see pins of other restaurants on the site, along with all of the preset bart stations.

Is this impossible to do, or can I have preset locations for all bart stations? Can each map show locations from other posts, or restaurants nearby, as well?