The rest is almost trivial. Go back to Inkscape again and create four new layers called "City Locations", "City Names", "Place Locations", and "Place Names".
Turn all layers except for the background image invisible. To increase contrast for the city and place locations, turn the Opacity of the background image layer to 70% or so (but be careful, because then you'll have to cycle the image through GIMP again to remove the transparency of the image).
Create two small black circles - one with a black filling, and one without. Copy and paste the first one to the "City Locations layer" to all locations where you want cities. Copy the second one to the "Place Locations layer" to all locations where you want to place unique sites.
Now you only need to label these sites with the Text tool in the City Name and Place Name layers. I recommend using different font sizes to distinguish the two - I used a size 12 font for cities and 10 for place names. Export the image as a png, load it into GIMP, add a blank white layer below it and save it again - and you are done!
And if you want to add new cities or locations, or want to move existing ones around, then you can easily do those changes in Inkscape without altering the background image…