While defining the projection for a new feature dataset, it occurred to me that I have not defined a z coordinate in a while. Well, I have some field data now with elevation (z values). Out of curiosity, why or when would I need to define a Z coordinate system?

Here's whats bothering me. If the projection is the same when the data was collected (x,y,z), do I still have to create a z coordinate in arccatalog? I mean the xy coordinate defined should cover this as well...correct? considering mean sea level does not change.

I would appreciate some simple scenarios why a z coordinate would be required in addition to an existing x,y coordinate already defined.

Thanks for taming my GIS curiosity.

Here's whats bothering me. If the projection is the same when the data was collected (x,y,z), do I still have to create a z coordinate in arccatalog? I mean the xy coordinate defined should cover this as well...correct? considering mean sea level does not change.

I would appreciate some simple scenarios why a z coordinate would be required in addition to an existing x,y coordinate already defined.

Thanks for taming my GIS curiosity.

whitepaper for the details, but simply put, *every* layer in ArcSDE has a coordinate

reference, which encompasses the coordinate system, the precision, the false offsets

and scales for the X/Y, Z, and M dimensions, and the tolerances for those dimensions.

The default offset and scale for the Z dimension are 0 and 1 (respectively), meaning

you could not capture data below sea level and only at 1 unit intervals. Therefore,

you need to define a Z component on the coordref any time you intend to store

coordinates with a Z dimension (that is, a Z value with *each* coordinate, not a

single "ELEV" attribute property for the feature).

- V