Help Distance matrix matrix API - Google Maps

I would like to know if with the distances API - Google Maps it is possible to calculate the distance of a city among others at a single time.

For example: calculate the distance from New York to Paris, from New York to Peking, from New York to Madrid?

And if not, how can I do with php go taking the answer from the following URL and keep only the KM:

link

{
    "destination_addresses" : [ "Rio de Janeiro, Rio de Janeiro - RJ, Brasil" ],
    "origin_addresses" : [ "Porto Alegre, Porto Alegre - RS, Brasil" ],
    "rows" : [
    {
        "elements" : [
        {
            "distance" : {
                "text" : "1.570 km",
                "value" : 1570193
            },
            "duration" : {
                "text" : "18 horas 5 minutos",
                "value" : 65097
            },
            "status" : "OK"
        } ]
    } ],
    "status" : "OK"
}

I need this to later verify if there is a distance of less than 50km between one location and another.