Background: I have an original shapefile with points that map just fine. I want to use these points to map other data (one point to many observations) that can be joined to the points with a field in the .dbf. (The "relate" functionality has not worked for me, and it seems like a ridiculous pain to fight with the software to do something I can do in a relational database in 30 seconds.) I thought instead to compute the X,Y for the points, output the .dbf as a text file, do my manipulations in other software, import the manipulated file, map the points, save as a shapefile, then do my geographic analysis.
What I did: Open the attribute table, create fields called X and Y, calculate corresponding geometry (using decimal degrees) using the coordinate system of the data source. Checked to see that the results match the coordinates of the mapped points. They do. Export the attribute table to a text file and when it asks if I want to add the exported table, say "Yes". Right click on table and go to "Display XY data." Note that the PCS and GCS are the same as the data source. Specify field X for X and field Y for Y. Map the data.
Problem: The points are in North America and map to near the equator. I'm attaching a graphic showing for one observation the X and Y fields in the data file and the X,Y of the mapped point. They don't match. No transformations are set. The data frame coordinate system and the ones for the attribute table and new table are the same (NAD 1983 UTM Zone 15N).
Plainly, I'm doing something wrong, but I don't know what it is. Help?