Soy un camino situado entre altas masas naturales. Elimina mi primera carta y tienes un camino situado entre las masas hechas por el hombre.

¿Qué soy yo?

Explanation:

This is a riddle that makes sense in English language but not in Spanish.

The translation is:  

I am a path located between high natural masses. Delete my first card and you have a path set amongst the man-made masses.

What am I?

Two high natural masses are two mountains.

The path between two mountains is called valley.

If you delete the first letter of valley you get alley, which is a passageway between buildings. And, of course, buildings are masses made by men.

Thus, the answer to this riddle is valley.

a. the astrolabe could determine the correct latitudinal location of the ship