If your measurement on the map is 3 5/8 inches, that would be 3.63 miles on the ground. "1 inch equals 1 mile"), determine the distance by simply measuring it with a ruler. For example, if the scale says 1 inch = 1 mile, then for every inch between the two points on the map, the real distance on the ground is that number in miles.
If the scale is a verbal statement (i.e. It might be pictorial-a ruler bar scale, or a written scale-in words or numbers. They are typically located in one of the corners of the map. Find the scale for the map you're going to use. If the line that you're trying to measure is quite curved, use a string to determine the distance, and then measure the string.
Use a ruler to measure the distance between the two places.