Un map, il ne manque plus que le reduce

gistfile1.js

map_closest
function map_closest() {
    var pitt = [-80.064879, 40.612044];
    var phil = [-74.978052, 40.089738];

    function distance(a, b) {
        var dx = a[0] - b[0];
        var dy = a[1] - b[1];
        return Math.sqrt(dx * dx + dy * dy);
    }

    if (distance(this.loc, pitt) < distance(this.loc, phil)) {
        emit("pitt", 1);
    } else {
        emit("phil", 1);
    }
}