api_controller.js

// http://localhost:4000/api/postcodesNear?postcode=4101&range=2

action('postcodesNear', function () {
    var earthRadius = 6378;
    var qPostcode = req.query.postcode || 4101;
    var qRange = Number(req.query.range) || 2;

    Postcode    .findOne({ 'postcode': qPostcode })
                .run(function(err, postcode) {
                    if (err) send(err);
                    else {
                        nearby = postcode.near(qRange, function(err,postcodes) {
                            if(err) send(err);
                            else {
                                postcodes.documents[0].results.forEach(function(location){
                                    location.dis = location.dis * earthRadius;
                                });
                                send(postcodes.documents[0].results);
                            }
                        });
                    }
                });
});

schema.js

    var PostcodeSchema = new Schema({
        postcode:       { type: String, required: true, index: true },
        locality:       { type: String, required: true },
        state:          { type: String, required: true, enum: ['ACT', 'NSW', 'VIC', 'QLD', 'SA', 'WA', 'TAS', 'NT'] },
        loc:            [],
        lat:            { type: String },
        lon:            { type: String }
    });

    //PostcodeSchema.index({ 'loc': '2d'}); 

    PostcodeSchema.methods.near = function findNearby (qRange, callback) {
        var earthRadius = 6378;
        var range = Number(qRange) || 2;

        return this.db.db.executeDbCommand({
            geoNear : "postcodes",
            near: this.loc,
            spherical: true,
            maxDistance : range / earthRadius,
            includeLocs : true
        }, callback);
    };

    var Postcode                 = mongoose.model('Postcode', PostcodeSchema);
    Postcode.modelName           = 'Postcode';
    module.exports['Postcode']   = Postcode;