# What projection is used in Argentina cadastral maps from 1901?

I am looking to georeference and digitize the cadastral maps for Argentina from 1901 and I need some help in determining the projection which was used in the creation of this maps.
For more detailed maps I can use land marks and roads but in some maps I really need to use the grid from the map I have no idea on the projection and google does not offer any help on this.

Hoya No 62 notes that the observatory of Cordoba is 64° 12' West of Greenwich, and Hoya No 54 shows the prime meridian going through Buenos Aires is 5° 49' 40" East of Cordoba.

So the prime meridian is 58° 22' 20" or -58.372222 West of Greenwich.

Based on the Campo Inchauspe datum used later in Argentina, you can build a custom CRS like

``````+proj=longlat +ellps=intl +pm=-58.372222 +towgs84=-148,136,90,0,0,0,0 +no_defs
``````

to georeference the images against.

You only get 8 grid crossings per map, so with using Thin Plate Spline, the result is not very accurate at the map borders. It might help to stitch two unreferenced maps together (after cutting off the collar) to get better georeferencing results.

• Great to see how you built a custom CRS. I did not know how to state `+pm=-58.372222`. Do you know where could we find the proper documentation to write custom CRSs? It will make your answer even better – Marco Nov 30 '18 at 8:45
• Just read the docs: proj4.org/usage/projections.html – AndreJ Nov 30 '18 at 14:58

The good news: there is no a projection, they are geographical coordinates, i.e., latitude and longitude.

The bad news: who knows where the zero meridian or Prime Meridian is?

It seems to be around 58° West, which is around Buenos Aires and make sense for a map from Argentina at that time.

• If you'll look on on page 47, lower right corner, there is a notation called "Este de Coroda". Would Coroda be Cordoba, which kinda has a central location in Argentina and it would make sense to take it as a central meridian. If that is the case, then the 4 degrees, 49 minutes and 40 seconds would mean the distance from the central meridian of Cordoba? What is the deal with that "H"? – alecsx Nov 29 '18 at 15:41
• I read "Este de Cordoba" somewhere. Why 1° is 2" is a nice quiestion, no idea. – Marco Nov 29 '18 at 16:13
• The H value is the time difference between local time and Cordoba time (with 4 minutes per degree). – AndreJ Nov 30 '18 at 8:15
• Yes, 4 minutes for degree makes sense, but it says 2 minutes (at least in the map I saw) – Marco Nov 30 '18 at 8:39
• Simply because Cordoba is not on one of the imprinted meridians, but somewhere between 6° and 5° West. So 5° West is about 3 minutes off against Cordoba time, 6° less than 1 minute. – AndreJ Dec 2 '18 at 14:38