This question refers to the differences in latitude and longitude values between NAD27 and WGS84 for Washington State. If I create a point using GCS NAD27, and populate the attribute table with lats and longs based on the points datum, and then change the data frame to WGS84 and I populate another two attributes with lats and longs using the data frame's WGS84 spatial reference system, the coordinates are the same.
Why are the values the same? Shouldn't there be a shift if the X and Y values that reflects differences in the datums?

  • Did you set a geographic/datum transformation in the data frame? Look for NAD_1927_To_WGS_1984_79_CONUS (or 85; I'm not at work to check). Then you would want to use calculate geometry with it set to use the data frame's coordinate system.
    – mkennedy
    Aug 3 '16 at 22:40
  • I didn't reproject the data itself. I used the calculate geometry option on an opened attribute table. No transformation is required there.
    – GBG
    Aug 3 '16 at 22:46
  • Why, yes, it is.
    – mkennedy
    Aug 3 '16 at 22:47

I created a csv file with a point falling in Washington ...

id, latitude,longitude
1,46.898861, -121.064639

... and added it to the map as a table.

I created an xy point event layer designating the datum as NAD27.

Geographic Coordinate System:   GCS_North_American_1927
Datum:  D_North_American_1927

I set the coordinate system for the data frame to WGS_1984_Web_Mercator_Auxiliary_Sphere. With a transform of NAD_1927_To_WGS_1984_79_CONUS.

From the same csv table, I created a second xy point event layer, but this time choosing:

Geographic Coordinate System:   GCS_WGS_1984
Datum:  D_WGS_1984

I measured the distance between them using the measurement tool: 135 meters.

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