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several ways:

1. level 11 land tech (armies can then explore terra incognita) and I believe level 16 in navy tech
2. Random event that will give you a conquistador or explorer (it happens, trust me)
3. exchange discoveries with other nations

One way or another, you will get the info you need.

have fun
 
Level 21 naval tech actually.

And there are a few more options:
1. If you win a naval battle, there is a chance that you might steal their rutters.
2. If you conquer enemy capital, you'll get your maps as well. I'd suggest Holland if you're a German minor.. they get the Spanish maps and are easier to conquer.