Just a little mathematical exercise in geography, namely the use of longitude and latitiude coordinates to calculate the distance between two given cities. You can obtain the coordinates for just about any earthly city from WWW.ASTRO.COM. The coordinates are in a format like 35n13 (35 degrees, 13 minutes north). The north/south indicator makes this a latitude. This value has to be converted to radians. The southerly direction is negative.
The same goes for longitudes, which have an east/west indicator. The westerly direction is negative.
You can expand the dictionary with additional cities, just stick with the format used in the code snippet.