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Converting projection of shapefile results in inaccurate measurements.

Question asked by on Nov 1, 2017
Latest reply on Nov 1, 2017 by



In ArcMap I am converting a shapefile's projection to the "North America Albers Equal Area Conic Projection." Whenever I do this, my map projects correctly but whenever I look at the measurements, they are incorrect. 


Here are my steps. I open ArcGIS, import a STATES.shp that begins with the GCS_North_American_1983 coordinate system, go to display view, and add a scale bar.

As you can see here, the display in miles is correct.

Then, I convert the projection using ArcToolbox --> Data Management Tools --> Projections and Transformations    --> Define Projection. I then select STATES.shp as my input dataset and select Projected Coordinate Systems --> Continental --> North America --> North America Albers Equal Area Conic as my output coordinate system. I select OK, then notice the changes to the map that ArcMap has made.

As you can see, the projection has changed visually but the measurement is way off. I am not understanding why it's doing this. Shouldn't the coordinates and measurements convert correctly? Is there an error in my file? Is there a way to resolve this by editing the metadata? I am new to ArcGIS and would appreciate any help.


Thanks in advance


PS if this is posted in the wrong section can a moderator please correct it