ISO defination

Isometric Projection at Wikipedia.

Simply put, the view needs to be--

1) Orthographic (ie, no perspective)
2) ~35.264 degrees above the horizon
3) 45 degrees around the vertical axis, relative to the tiles

Anything else is technically not an isometric perspective. Games like Diablo 2 are called isometric, but if you really want to pick nits, they aren't isometric, since they use a 2:1 tile ratio which can only be achieved with an angle of 30 degrees above the horizion (IIRC); thus making it slightly not isometric. [grin] The 2:1 ratio is used because it is so simple to program and create assets for; and it is convenient to call such games isometric, so we do. Just beware of polluting the usage of the term by trying to apply it to incorrect projections.

okay it uses 2:1 tile but there is also an option to change its view to perspective and i think it is because of it is based on 3d data not on 2d. will we still call it an isometric because it is not the ratio it is actually the 3d data. and if it is not an isometric where we will put it.

just a little bit of info:
the 2:1 ratio or 30 degree angle is generally used for technical drawing too. you know set squares? 30 degree angle there.
just saying there's absolutely nothing wrong with doing "isometric" that way ;)
to answer your last question:
the perspective view (as VertexNormal mentioned) isn't isometric - isometric is a "flat" representation of the tiles - i.e. the tiles don't look different further away, they all look the same width/height throughout the whole map. this is the orthographic setting that VN also mentioned - i believe it stops the perspective style or look of the scene when rendered in a 3d API.
(feel free to correct me if i'm wrong VN)
actually, here's an example from my map editor:

this is a 2d drawn map, but provided a 3d map looks similar (just 3d rectangluar prisms as tiles), it'd be fine.
hope this all helps

later