How to find the projection of an image?

Question

Instead of georeferencing the image and deforming it, I'm trying to find the projection used by the author of the image.

I've got tens of these distribution maps to digitize. The idea is to avoid image distorsions and to find only the parameters of pixel dimension and top-left corner coordinates to move maps in the correct position. To do that I need the original coordinate system.

I used ArcGis 10.2.1 to compare and customize different coordinate systems, but no one matched and the variable parameters for every projection were few. I used Flex Projector, but it's not possible to import and overlap an image for a comparison, moreover the software exports many parameters I cannot use in a desktop GIS. Using EPSG codes in Qgis would take me months to find the proper one.

Any ideas how to solve it? or which GCS could fit better?

Answer 1

Finding the "right" projection is a rather time-consuming process.

The best way would be to ask the map creator (if he still lives), but I guess this is not the answer you want.

So take a look at available map projections, e.g. at http://www.radicalcartography.net/index.html?projectionref, and compare the shape of the degree grid with your example.

At your map, 100°E is the only unbowed meridian, so that should go through the origin of the projection.

The EPSG codes used by QGIS only have little use for you, as they cover only projections used by surveyors, and not exotic projections to fit half of the world. But QGIS custom CRS can display a lot more projections. Unfortunately not all, because projections without formulas for the inverse projection are omitted.