This was a bit of an experiment trying to make a night version of my Ferryhill map. What I mainly did was to duplicate the image and make the top one black and white. There are a couple of ways to do this, I usually do it by applying a gradient map layer that goes from black to white and then merge the top layer with the gradient map layer. The gradient map layer makes the contrast really nice and I like that.
I then added a layer mask to the top layer (the black and white version of the picture) selected the pen and changed the opacity of the pen to around 30-40%. The size of the pen depends on the size of your picture. I then started to paint in the layer mask with black. This will make the parts where you paint invisible, which means that the colour version shines through and look like lights in the night.
When you’re satisfied with the lights you’re painting in add a new layer mask layer called photo Filter. Choose filter Blue and change the opacity of the layer to around 60%. This will make the night look a bit more bluish, which I like. If you like to have the night blacker, don’t add this layer.
That’s much about it. You might have to fiddle around a bit with the different layers opacity to get the right feeling. Good luck 🙂