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I have a historic paper map for the Indian Sub-continent which has been scanned. The Map is in Albers Equal Area Conical projection, and has the latitude and longitude grid on it.

I was trying to georeference in the projection of the source, but I do not have all the required parameters for this projection. Only the two standard parallels are noted on the map. I don't know the Central Meridian or the Latitude of origin, or the datum for that matter.

What should be done in this kind of situation? Since this is a map which spans 4000km by 4000km, I don't really think it is possible to get any kind of high accuracy output. I was thinking of georeferencing it in wgs84 Geographic coordinate system.

Is this a good idea? Or is there something else which you would suggest?

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2 Answers

up vote 2 down vote accepted

When viewing anything in a geographic coordinate system in GIS software, it is not unprojected. It still has to be displayed on your 2-dimensional computer screen. Usually this uses a latitude/longitude grid in a type of equirectangular projection known as plate carrée. This would produce a very strange result in your georeferencing, since your source map is a conic projection and the GIS software would be a cylindrical projection.

I would recommend making your best guess of the projection parameters. There's an Albers projection for India on SpatialReference.org that has some parameters you might want to try.

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It does not have to be georeferenced in the original but it would have to be "rubbersheeted" if it isn't.
In other words as dmahr suggested it is best.
You can probably find the "localized" albers projection.
Here are some that might be appropriate in the arcgis system.

Image1

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