How to accurately isolate Europe from a rasterised world map image

Question

There is a World Map of Autumnal UV provided for educational purposes by Nina Jablonski (created by George Chaplin) that I want to analyse.

In particular, I want to use Python to statistically analyse the colours found in Europe as defined by the United Nations Statistics Division. For this to work I need a way to isolate the world map to only contain the countries of Europe.

The best idea I have to achieve that would be to find a similar world map with borders, use Photoshop to overlap it with the map of Autumnal UV and remove the areas outside of Europe by hand.

At this stage, I am finding it hard to find a world map with borders that uses the same projection. Although Nina's website states the world map uses "Hammer-Aitoff projection" the map itself looks like it uses Eckert VI projection. While I have found a world map with borders using Eckert VI projection, I struggle to get everything lined up without stretching the image.

Does anyone know which projection the Autumnal UV world map uses or have a better idea of how to achieve my goal of accurately isolating Europe from a world map?

Answer 1

Your goal can be achieved with a fairly straightforward clipping operation using GIS software such as QGIS. The main challenge will be to geo-reference the autumnal UV map, which is a non-referenced .jpg. Once you've accomplished that, you load the raster layer and vector layer outline of Europe (Natural Earth would be one place to find this.) The GIS program can reproject the a vector layer to match the projection of the UV map. You then use the clipping function to remove those portions of the UV map outside of Europe.

I would caution you that unless you can find a higher resolution version of the map you are unlikely to find much interesting in analyzing the map. The pixels of the UV intensity are appear to be 50-75 miles across. The linked map has no legend indicating UV intensity associated with each color.