I am piecing together the land owners in an East Georgia militia district
and wanted to find out more about the impact of magnetic declination when
plotting a map like this.
First, how do I determine the approximate magnetic variation for my area
during the years 1783-1823? I found a government website that calculates for
the years 1900-current, and I found one site that has values for each decade
in each early state's modern capitol, including Atlanta. Unfortunately, none
of the state grants during this period include magnetic variation values.
Second, if I am able to reconstruct historical magnetic declination values,
are there any pitfalls I should be aware of when using them to adjust the
orientation of my plots? Is it as simple as just rotating the plot a certain
number of degrees?