In Mexico City, our Amigos D.F. return to tell us something about arquitectura (architecture) in el D.F. (in Mexico City, that is). Indicating a nearby building, we hear:
...abajo es una zona comercial, todo lo que vendría a ser la planta baja... y arriba, allá, son este... departamentos... residenciales.
"...below it's a commercial area, everything that would be the ground level... and above, there, are... apartments... residential."
[Captions 17-19, Amigos D.F. > Arquitectura]
Despite the rambling nature of this unscripted dialogue, it's easy enough to understand that there are commercial businesses on the ground floor of this building and residential apartments above. If the building has an elevator, pressing the p.b. (planta baja) button will take you to street level.
Push "1" in the same elevator and you'll end up on what's referred to as the "second floor" in New York or Miami. You see, in Spain and in Latin America, "l primer piso is "the first floor *above* the ground level."
So, let's take this language lesson up a step. Say you want to visit your Mexican friend in his apartment up on "2." That's el segundo piso ("the second floor"). You see, you rarely hear la segunda planta or la primera planta outside of architectural drawings. In everyday speech, you'll usually hear pisos"instead of plantas describe floors 1 through, well, the sky's the limit.
A final note on arquitectura: Departamento is the word of choice for Latin American apartments. Meanwhile, over in Spain, you'll typically hear apartamento.