where does map_coords go

map_zoom.js

var models_module = require(MVC_MODELS);
var Gate = require('util/gate');
var map_reduce = require('./zoom_back_map_reduce');

function _zoom(err, map_coords_model, map_id, map_data, map_mode, callback) {
    console.log(__filename, ': _zoom() ##################');
  //  var args = Array.prototype.slice.call(arguments, 0);
  //  console.log('arguments: ', args);
    //FIRST ACTION : knock all the zooms back one 
    try {
    //    console.log(__filename, ': _zoom: map_coords_model = ', map_coords_model, ': map_id: ', map_id);
        //THIRD ACTION: put the zoom points back to the map_coords collection

        function _insert_new_data() {
            console.log(__filename, ': _insert_new_data');
            gate = new Gate(callback);

            function _insert_row(err, doc) {
                if (doc) {
                    var new_point = {
                        map: map_id,
                        i: doc._id.i,
                        j: doc._id.j,
                        height: doc.height,
                        position: new Array()
                    };

                    new_point.position.push(doc.position[0]);
                    new_point.posiiton.push(doc.position[1])

                    gate.task_start();
                    map_coords_model.insert(new_point, function() {
                        gate.task_done();
                    });
                } else {
                    gate.start();
                }
            }

            function _insert_rows(err, cursor) {
                cursor.each(_insert_row);
            }

            models_module.model('map_zoom', function(err, mz_model) {
                mz_model.all(_insert_rows, {
                    cursor: true
                });
            })
        }
        //SECOND ACTION: note the zooms into a temporary collection

        function _create_zoombacks() {
            console.log(__filename, ': _create_zoombacks');

            var mr = map_reduce(map_id);
            map_coords_model.config.db.runCommand(mr, _insert_new_data);
        }

        //FIRST ACTION UPDATE:
        var zoominc = { "$inc": { zoom: 1 } };
        var filter = { map: map_id };
        
        if (!map_coords_model){
            map_coords_model = arguments[1];
        }
        
        console.log(__filename,' : MAPCOOORDSMODEL:');
        console.log(map_coords_model);
        map_coords_model.update(zoominc, _create_zoombacks, filter);
        
    } catch (err) {
        if (err) {
            console.log(__filename, ': err ', err);
        }
        throw err;
    }
} // end _zoom

where is map_coords going?

/Users/bingomanatee/Documents/Arena_colles/node/controllers/map/actions/zoom_back.js : zooming back ==================== from 4ddfb7d9ba36d54fad000001
BSONifying 4ddfb7d9ba36d54fad000001 , out = 4ddfb7d9ba36d54fad000001 : type = object
BSONifying 4ddfb7d9ba36d54fad000001 , out = 4ddfb7d9ba36d54fad000001 : type = object
/Users/bingomanatee/Documents/Arena_colles/node/models/maps/zoom_back.js : id: 4ddfb7d9ba36d54fad000001 , oid: 4ddfb7d9ba36d54fad000001 : zoom back start
NOT initializing model map_coords on_load
/Users/bingomanatee/Documents/Arena_colles/node/models/maps/zoom_back.js : _zoom() ##################
/Users/bingomanatee/Documents/Arena_colles/node/models/maps/zoom_back.js : MAPCOOORDSMODEL:
{ name: 'ac.map_coords',
all: [Function],
count: [Function],
_as_oid: [Function],
string_id: false,
get: [Function],
find_and_delete: [Function],
delete: [Function],
put: [Function],
insert: [Function],
soft_delete: false,
update: [Function],
find: [Function],
data: [],
config:
{ db:
{ databaseName: 'ac',
serverConfig: [Object],
options: [Object],
bson_serializer: [Object],
bson_deserializer: [Object],
connections: [Object],
state: 'connected',
pkFactory: [Object],
strict: false,
collectionName: undefined,
queryOptions: undefined,
numberToSkip: undefined,
numberToReturn: undefined,
query: undefined,
returnFieldSelector: undefined,
db: [Object],
_events: {},
version: '1.8.0' },
coll:
{ db: [Object],
collectionName: 'map_coords',
pkFactory: [Object],
hint: [Getter/Se
node.js:183
throw e; // process.nextTick error, or 'error' event on first tick
^
TypeError: Cannot call method 'update' of undefined
at _zoom (/Users/bingomanatee/Documents/Arena_colles/node/models/maps/zoom_back.js:69:26)
at /Users/bingomanatee/Documents/Arena_colles/node/models/maps/zoom_back.js:86:13