How I made the composite Image of the subway

I made this composite Image by using a program called Gimp 2. This program was a little bit hard to get use to but after practising with it I got use to it. What Gimp 2 does is that it merges two pictures together to make one.
To make the composite image I had to first find two picture, one of the derry city, and the other of a subway. I found two pictures and here is what they look like:

After finding the right pictures I started merging them together. First I got the subway picture and started deleting the parts of the pictures that I didnt want. I did this with a tools from the toolbar of the Gimp 2 program that it gives you. here is the toolbar which I used;

To merge the picture I had to make the parts of the picture I didn't want to go invisible. I did this by using a tool called "select contiguous regions"and erase. This clicks on areas of the picture and then you click on erase to make them invisible. After making all the parts of the picture I didn't want invisible I then dragged it on to the other picture of the Derry Walls and I had to merge it into the picture to make it look real. I merged it by using different tools on the image of the subway. I cropped and resized the image. by doing this it made it fit in with the picture which helps to make the two pictures turn into one. This is how I designed my composite Image through using Gimp 2. I found this hard to do but by reading through the tips that Gimp 2 gave me I could work through it and merge the pictures together.