They don't appear exclusively in a map, but are randomly added in maps introduced after the WarChiefs expansion, along with other mines. They are similar in appearance to Silver Mines.
- Ironically, while tin is the rarest mineral in Age of Empires III, it is also the least valuable.
"As in the case of copper, people have gathered and mined tin for thousands of years. It key value to the ancient world was in combination with copper, the creation of bronze - an alloy widely used for weaponry and art.
Because of its ability to inhibit corrosion, tin has long been used to coat steel and other metals. Indeed, the commonly referred to "tin can" is actually made from steel, with only a minimal tin plating.
Even though scarce, tin is found all over the world and on every continent. Most tin processed today is mined in Southeast Asia."