Now that you know how to draw maps, and set markers, let's do some "map math." Let's compute
the distance between two points on the map. We'll reference the two points by their
latitude and longitude, like this $(lat_1,lng_1)$ and $(lat_2,lng_2)$.
To start, let's use Los Angeles (34.1,-118.25) and New York (40.7,-74.02).
Next, you'll need the radius of the earth (in kilometers), which is 6,371 km. To find a distance,
$\Delta lat=lat_2-lat_1$ and $\Delta lng=lng_2-lng_1$.