I use topographic maps from MyTopo.com with UTM grids and Lat/Long tics printed on them.
Take a ruler and connect the tics for Longitude. Those lines will be true north.
Question #1: Do longitude lines (north-south) always lie on true north? Or might they be slightly off? Maybe something to do the datum model?? These are hard to work with on my maps since I only have longitude tics printed, but I'd still like to know.
Yes, by definition, Longitude lines run exactly North-South. See above regarding connecting the tics.
Question #2: Are the left and right edges of the MyTopo maps always true north? I think these have the highest chance of being true north, but I'm not 100% sure of that. I'm waiting - hoping - to hear back from MyTopo on this question.
Don't know. MyTopo will need to answer that one. If there is a Longitude tic at the corners, compare at the top and bottom. If on one side Longitude is the same on the top edge and bottom edge, then that edge is true N-S.
I've seen some people recommend orienting the map to true north using the TN symbol lines, but they are kind of short for easy use.
I'd be careful with that one. I think sometimes the little symbol declination diagram is just that...diagrammatic? Especially when for example TN & MN are only a couple of degrees apart it could be tough to show on the diagram without exaggeration?
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