2

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?

3
  • 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
3

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.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.