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Why do different geographic coordinate system have no affect on point locations in event layer

Question asked by ChrisHalchuk on Dec 17, 2018
Latest reply on Dec 17, 2018 by ChrisHalchuk

Hello,

I have a table with 7000 records representing point locations spread over a 70 km east-west and 50 km north-south extent. The table has coordinates in decimal degrees for each record contained in 2 fields called Longitude and Latitude. Because the source data does not provide any indication of which geographic coordinate system the points use, I decided to try testing a few common ones to see which system seems to line up best with my other layers. I am using ArcGIS 10.5.1 and my tabular data is contained in a file geodatabase.

 

Therefore I added the table as 3 separate point event layers and chose geographic coordinates using WGS84, NAD83 and NAD27 to test things out. However, I was surprised when I zoomed in as much as possible, that there was absolutely no difference in where the points were displayed between all three coordinate systems. The points are simply meant to fall within property polygons, and they do seem correctly located, but I was expecting to see differences between the geographic coordinate systems - but I do not. I saved each of the 3 point event layers to a separate point feature class within the file geodatabase just to be sure the even layers were written permanently to file in the 3 different geographic coordinate systems. There is also no variation in corresponding point locations in these 3 feature classes.

 

I know there should be a significant difference between NAD83 and NAD27 datums - on the order of 10 to 30 metres in my map area, but the points have identical positions.  Is this an error or is there something I am missing? Should there not be a difference in where the points are displayed when using different geographic coordinate systems for an event layer.

 

Thanks in advance,

Chris

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