Ask Baldor Iron-Shaper where you can find this Ancarion guy. He tells you that the elves have a ship. They took Baldor there and showed him the map. You will find it on the northern coast of the island. Baldor begs you not to let Ancarion make his weapons. Kill Ancarion or let him live, but take the map from him. It belongs with the Skaal.

Baldor tells you he will return to the village (Skaal Village). When you have the map, bring it to him there. This marks the objective "Search for Baldor Iron-Shaper" as completed, and starts the next objective which is to retrieve the Stalhrim Source Map. The location of Ancarion's ship is on the North coast of the island. See map below for help finding it:


The discovered closest point of interest to the destination is White Ridge Barrow, so fast travel there if you have unlocked it, otherwise fast travel to the nearest available marker and start your trek from there. Arrive at Northshore Landing, and talk to the Thalmor Soldier near the ships there. He tells you that you are trespassing, and strongly suggests you move along.

Your dialog options are:
I have business to discuss with your leader
You will pay for your crimes against the Skaal. Prepare to die!

You might as well go with the second option and kill them all. Then, kill Ancarion who is on the ship that is docked nearby. Loot the Stalhrim Source Map from him. This completes the objective "Retrieve the Stalhrimm Source Map" and gives you your next objective, "Talk to Baldor Iron-Shaper"