Download this >>> Map.web and double click to have Xara open it. As you have only just started with Xara you will need help in knowing what does what and how it was done.

Expand the Page & Layer Gallery (right hand side of screen)
Click the red padlock next to Pasteboard Background to allow editing
Approx in the middle of the map click and drag sideways. You will see there is a simple black rectangle with an 85% transparency
Drag and drop your own picture directly onto the picture of the map. This will replace the map I used
Use the Preview (eyeball icon top task bar) and decide if you need the dark rectangle or not. Re-position if you do, delete if you don't

Have a play around and ask how things work if you can't figure the rest out. It's unlikely you will be able to do this without asking as you are very new to Xara and still thinking in terms of Serif.

The end result will (should) look like this...

Click image for larger version. 

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