I have GCS shapefiles that I loaded back into an SDE state plane database. The database shows that they are in State Plane, not GCS. Are they actually in the correct state plane or are they still in GCS and will be distorted or shifted in some small way?
jbalk's answer is the means to intentionally convert from your GCS to State Plane.
The direct answer to your question is that unless you intentionally changed/transformed the projection into State Plane the data is probably still in GCS but stored 'thinking' it is in State Plane. At that point, a feature at lat long 30,90 will be showing close to 0,0 in the State Plane projection.
You can set the coordinate system for a file without it really being projected into that coordinate system.
- Copy the original shapefile.
- Use the Project Tool to convert to the state plane zone.
- Load it into the database.
Open ArcMap and add the two layers from the ArcSDE database.
They should line up because ArcMap will have set the data frame's coordinate system to one of the layers, and the other layer will be projected on-the-fly to the data frame's coordinate system.
- Open data frame properties and select the Coordinate System tab.
- Click the globe button and select Clear.
If they're in coordinate systems as different as a geographic (lat-lon) one and a state plane one, they won't overlay anymore.
Similary, look at the extents of both layers. The original data will have extents in decimal degrees, while the state plane layer should have much larger coordinate values (in meters or feet (US or international)).