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I am trying to trying to calculate the bearing of a line relative to magnetic north, but cannot find documentation on what ArcGIS Pro references when providing direction values. Ideally, I would like to calculate the bearing of the line directly in magnetic north or in true north and use the declination to convert the values to magnetic north.

The values provided by the Measure Direction Distance vary when the map projection is changed, so clearly these values are referencing some sort of grid north based on the coordinate system.

Using Enable COGO and Update COGO populates a Direction Field in the attribute table, but the documentation for these tools does not specify what the direction is relative to (i.e., grid, true, or magnetic north). However, it appears these tools also reference the projection of the layer itself in some way, as the Direction values change when calculated on copies of the line layer with different projections (e.g., 0.66 deg in UTM 15N and 4.42 deg in UTM 16N).

I'm open to other ideas if there is a simpler way to measure a bearing relative to magnetic or true north.

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