The following description is from dminoz's "Daily Imperialist". (Authorship and copyright not certain, and his e-mail seems to be dead; if he or anyone else claiming authorship thinks this should not be here, let us know.) :
- The Explorer is arguably the most important civilian unit in the opening stages of the game. The Explorer's priorities include locating sources of iron ore closest to the capital; finding copper and tin; prospecting for riches in the New World; and finding Tribal capitals. You also need an Explorer to conquer landlocked New World provinces.
- You're given a free Explorer to start with. Acquiring the second is a wise move but may be difficult at one of the higher difficulty levels. Ideally, you should have one Explorer uncovering the New World as the other continues to look for minerals on your home ground. Don't neglect the hills and mountains of Minor Nations; sometimes a mousy little Minor turns out to be a valuable trading partner following a discovery.
- At some point in time, there may be no more work for your Explorers. Don't dismiss them all, though -- set the to work on any New World territories newly won from other Great Powers. Chances are you'll find plenty of hidden treasures, often including riches that the computer missed.