This is was a Photoshop image I did to illustrate how Chinese national oil companies were active in Africa.
I’d tried recently many vector flags and country outlines solutions to similar illustrative quandaries and I thought this time it was nice to do it all in Photoshop.
I created the mask of the outline of Africa by copying the Blue Channel and adapting it to be a selection of only the part of the map that was Africa. Here is explained using Channels to make masks and selections on a similar image.
Once you are happy with the extra Channel, it’s a Cmd/Ctrl click on it to make it a selection then over to the layer you want masked and a click on the Add layer mask icon in the Layers palette. The beauty of this way of masking is that the mask can added to or subtracted from with the Brush tool(B) or even blurred to create the effect you want.
After this was done it was the usual playing round with layer blend modes to get the best effect. The top flag layer I had on Normal with an Opacity of 60% and under that I had another duplicate layer with a Hard Light blend mode. Underneath was just the original map image as a Background layer.