What kind of map? One that's created in chat, or an actual Map item? What factions plugin are you using? It would depend on how plots/homes are handled that determines how you should approach it. With the information you've provided, the most I can say is that you would begin by getting the player's position, plotting an area x blocks around them, and scanning that area for faction homes/plots, and marking them on the map.
If not looking for "physical" map in minecraft, but rather the one shown in chat, then look at this: FactionsPE/Collections.class#L41