4

I'm using ArcGIS.

I have a historical map from 1884. It has bathymetry information which I would like to compare to modern bathymetry models with as much accuracy as possible. I don't know what projection to use to retain the best accuracy for comparison.

I've tried georeferencing it once using a WGS_84 projection, and again using a NAD_83 projection for that zone (since this is a small area).Naturally, the map warps differently depending on which projection I've used.

A problem with this map as well, is that I can't space the GCPs very evenly across the raster because the entire bottom half of the map is water. So while I can get the top half georeferenced to fit nicely (using the roads, lighthouses and even some natural features), I'm afraid the bathymetry information will be incorrectly distorted. That's why I really want to choose the best projection.

Which one do you think I should use?

Do you have any ideas on how I can keep this most accurate?

enter image description here

  • 2
    Its unlikely that its perfectly accurate to a projection if its that old. You might find the best results by warping it to as many known points on land as you can – whatahitson Oct 20 '15 at 14:55
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    Besides which projection you are using, you should also consider which georeferencing-transformation method you are using. If you are using a higher order transformation then the lack of points in water will cause significant issues. For a carthographic map like this, 1st order transformation should be suitable. – Mikkel Lydholm Rasmussen Oct 20 '15 at 15:00
5

It seemed to me that the most reliable identical points are the intersections of the streets that are also visible in the aerial imagery: 12 x 5 blocks

I chose the following two identical points to define shift, scale and rotation: enter image description here

and the result is this: enter image description here

Also, here is the world file:

9.5796348501660056
0.0087429941810302191
0.008742994179871285
-9.5796348501606499
-7468807.2251652461
5634978.2160751447

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