Does anybody know which CRS should be selected when georeferencing a Falklands map made in 1961? The map itself says only:
Grid: UTM Zone 21 Projection: Transverse Mercator Spheroid: International Meridian of Origin: 57° West of Greenwich Latitude of Origin: Equator Scale Factor at Origin: 0.9996 False Co-Ords of Origin: 500,000 m. Easting, 10,000,000 m. Northing
Another question is, what coordinate values are more suitable to georef this map? It has both 6/7-digit UTM coordinates and lat/lon values. However when I create control points with lat/lon values from the map corners I get 10 to 20 pixels error in every point, and the resulting map does not exactly match the overlaid OSM layer. Could this be due to incorrectly selected CRS? if not, what else could be tweaked here?