I still have to figure out how to correct the "shift" in the overlay - it has to do with the map datums used on the old maps compared to today.  You see the same thing on the older USGS maps on the gmap maps when you compare them to a newer map (like myTopo maps).

The other thing I want to try and figure out is to make it so you can select which maps to use as the base and overlay maps.  I sort of have options to pick the base map, but I would like to expand that, and then have a drop down to select which historical overlay to use.  It is rather slow work, since it is all experimentation (try something different, render the maps, then see how it works), but it is interesting and very useful I think.

Thanks for the feedback.  Stay tuned.

I didn't study it too close, but the further south I went the more it seemed noticable.

A clear place to see it is the old skyline road towards Olallie.

And the 46 road shows on the wrong side of the river in spots.

To bad you can't just bump the table . . .

D 2

All I can tell you it is has to do with some very complicated math (there is a LOT of math used in maps).  I do know that the farther west you get, the worse the drift is.  What I did when I referenced the map was to use the coordinates of (mostly) the corners of the map. 

122 30' 00"     121 00' 00"

45 30'  00"      45 40' 00"

122 30' 00"    121 00' 00"

44 40' 00"      44 40' 00"

Those were the 4 corners I used to do the georefererncing.  The upper left is south a bit because that is where the map legend was, so I took the northernmost point I could reference.  I may try and reference by some other unique thing, like peak or something.  Or maybe I will try and reference via section lines, but I'm not sure that will be correct, since the datum is different.  I'm just going to have to experiment.

If anyone has experience in georeferencing maps and/or converting from NAD27 to WGS84, I would greatly appreciate any assistance.  This is ALL new to me and I'm trying to learn as I go.

Dare I say it but, an analog solution might be easier.

D 2

(Eagerly awaiting the digital imlposion.)

Yea, it would be, but it wouldn't be as cool (or as useful).  I'll get it figured out eventually....