Undefined coordinate system for map georeferencing

Question

Hello!

I’m trying to georeference a geologic map sourced from a paper. They do not state what projection they used when creating the map. I’m having a **bleep** of a time trying to find one that matches the geometry of the map. I’ve tried all of the typical projections for the map area (near Ornavasso, Italy). Any suggestions as to how to proceed with georeferencing when the coordinate system is not stated in the source material?

Thanks!

danretired · Answer

All I can suggest at this point is that the base information may exist on a published map and that the thesis map may have used it as a base.  Sorry

Alainamrg · Answer

Hi Dan!

Thank you for your reply. It is in raster format (.png). There are no reference grids or coordinates on the map. It is sourced from an unpublished PhD thesis.

There are some markers that I've been using in an attempt to georeference (e.g. the geometry of lakes and sparse rivers) but because they are not uniformly distributed and do not match the spatial projection i'm trying to tie them to, my map is becoming warped. The geometries of the lakes do not match any projections I've tried thus far. I'm attaching the map for reference!

Thanks Dan!

Screen Shot 2021-01-27 at 3.14.45 PM.png

danretired · Answer

I assume it is in raster format? (eg a *.tif, *.png)

Are there any reference grids or graticules on the map that can be used for locational information? (eg long/lat coordinates, UTM grid markings)

Georeference a raster to a referenced layer—ArcGIS Pro | Documentation

is one possibility...

If the paper map is sourced from a government agency, many locales  host digital versions of maps, so I wouldn't rule that out as a source of data in the first instance.