We can easily solve this by setting up a ratio. A ratio shows the relation of two numbers when compared to another set of numbers.
In this case, we know that 1 inch is equal to 500 miles, and we are trying to find how many inches are 650 miles. Therefore, we set up a ratio like:

Now, we must find out what we need to multiply "500" by to get "650."
500x=650
/500 /500
x=1.3
Since we need to multiply "500" by 1.3 to get "650," we know that we need to multiple our inches by 1.3 as well. This will keep the fractions equivalent.
1*1.3=1.3
Using the logic above, we can conclude that, on the map,
City A is 1.3 inches from City C.