Define Projection not working

[CarbonAmerica]

Hi everyone,

I've been having issues with defining projections for shapefiles with unknown coordinate systems. These shapefiles are exported via Petra and/or Kingdom, which are both geologic software programs. I have no problem getting them in, but once they're there, they show up in the middle of the ocean due to the the projection being undefined. I always go to the define projection tool and define it into the projection that is needed, but it never shows up in the correct spot. It usually shifts from being in the ocean near Africa to the Pacific off the coast of South America. Should I be selecting a Geographic Coordinate System or a Projected Coordinate System?

Is there another tool that I should be using? My coworker is able to get the tool to work correctly when she opens it up in a new project, and I'm the only one that doesn't have any luck. 

Please let me know your thoughts and potential remedies.

[MiniR]

are all the projections/coordinate systems the same in your project?

[DanPatterson · Accepted solution]

Calculate the x and y coordinates in the table (centroid will suffice for polygons/polylines) and look at them.

Do they look like projected coordinates? or do they look like decimal degrees?  

If the latter, then define it with a geographic coordinate system first then Project them if needed

[RhettZufelt · Accepted solution]

You need to define the projection that the data is in, NOT the projection needed.  That way, Arc can project on the fly to the "needed" projection. (or you can then re-project to the needed SR)

R_