How to best calculate the distance between two cities (Canada)?

i have a client who wants me to calculate the distance in miles between cities. I am doing project in PHP, javascript , i have been rea开发者_StackOverflow中文版ding about some long/ lat database but still not able to find where to start and what to use for it. Is there any web service i can query by passing two city names and it can return me the distance in miles or km? please help

http://code.google.com/apis/maps/documentation/javascript/geometry.html#Distance

Distance and Area Functions The distance between two points is the length of the shortest path between them. This shortest path is called a geodesic. On a sphere all geodesics are segments of a great circle. To compute this distance, call computeDistanceBetween(), passing it two LatLng objects.

You may instead use computeLength() to calculate the length of a given path if you have several locations.

To compute the area of polygonal area, call computeArea(), passing the array of LatLng objects defining a closed loop.

If you do not want to maintain a GEO db that maintains the lat/long to a place/city, then you can also use the Google API to retrieve the coordinates for an "address": http://code.google.com/apis/maps/documentation/javascript/services.html#GeocodingRequests

Another option is to use a variation of the Great Circle Calculator implemented in Javascript if you aren't a google fan:

https://gist.github.com/missinglink/ab7c8b9b8699622539986373e6237fd4

https://www.edwilliams.org/gccalc.htm

The non-API solution. This has the advantage you're not reliant on any third-party, which may go down, or cost you, or be rate-limited, slow with responses etc etc.

First convert your locations to lat/longs. You will need a db of cities and co-ords for this, but I imagine this can be found pretty easily. In the UK this data is available from various govt agencies for free. Then with the co-ords you can calculate the distance between them. The below is in java, but should be straight forward to port to javascript (or php):

public static double R_EARTH_EQUATORIAL = 6378137.0;
public static double R_EARTH_POLAR = 6356752.3;

// The shortest dist between two points on a globe. Lat/lngs are in RADIANS
public static double greatCircleDistance(double lat_1, double lng_1, double lat_2, double lng_2) {

    double d_lat = lat_1 - lat_2;
    double d_lng = lng_1 - lng_2;
    double lat_ave = (lat_1 + lat_2) / 2;

    double h = haversin(d_lat) + Math.cos(lat_1) * Math.cos(lat_2) * haversin(d_lng);
    return 2 * R_EARTH(lat_ave) * Math.asin(Math.pow(h, 0.5));
}

public static double haversin(Double x) {
    return Math.pow(Math.sin(x/2),2);
}

// Returns radius of earth at a given latitude
public static double R_EARTH(double latitude) {

    double a = R_EARTH_EQUATORIAL;
    double b = R_EARTH_POLAR;
    double x = latitude;

    double p = Math.pow((Math.pow(a,2) * Math.cos(x)),2);
    double q = Math.pow((Math.pow(b,2) * Math.sin(x)),2);
    double r = Math.pow(a * Math.cos(x),2);
    double s = Math.pow(b * Math.sin(x),2);

    return Math.pow(((p + q) / (r + s)), 0.5);
}

Since Google Maps is paid now. The best free alternate is using openstreetmap API either in JavaScript or PHP. You can get latitude and longitude of the cities using their geocoding web service. Here is sample site providing distance between two cities using openstreetmap.org APIs.