Function is not defined - uncaught referenceerror

Your issue here is that you're not understanding the scope that you're setting.

You are passing the ready function a function itself. Within this function, you're creating another function called codeAddress. This one exists within the scope that created it and not within the window object (where everything and its uncle could call it).

For example:

var myfunction = function(){
    var myVar = 12345;
};

console.log(myVar); // 'undefined' - since it is within 
                    // the scope of the function only.

Have a look here for a bit more on anonymous functions: http://www.adequatelygood.com/2010/3/JavaScript-Module-Pattern-In-Depth

Another thing is that I notice you're using jQuery on that page. This makes setting click handlers much easier and you don't need to go into the hassle of setting the 'onclick' attribute in the HTML. You also don't need to make the codeAddress method available to all:

$(function(){
    $("#imgid").click(function(){
        var address = $("#formatedAddress").value;
        geocoder.geocode( { 'address': address}, function(results, status) {
           if (status == google.maps.GeocoderStatus.OK) {
             map.setCenter(results[0].geometry.location);
           }
        });
    });  
});

(You should remove the existing onclick and add an ID to the image element that you want to handle)

Note that I've replaced $(document).ready() with its shortcut of just $() (http://api.jquery.com/ready/). Then the click method is used to assign a click handler to the element. I've also replaced your document.getElementById with the jQuery object.

How about removing the onclick attribute and adding an ID:

<input type="image" src="btn.png" alt="" id="img-clck" />

And your script:

$(document).ready(function(){
    function codeAddress() {
        var address = document.getElementById("formatedAddress").value;
        geocoder.geocode( { 'address': address}, function(results, status) {
            if (status == google.maps.GeocoderStatus.OK) {
                map.setCenter(results[0].geometry.location);
            }
        });
    }
    $("#img-clck").click(codeAddress);
});

This way if you need to change the function name or whatever no need to touch the html.

The problem is that codeAddress() doesn't have enough scope to be callable from the button. You must declare it outside the callback to ready():

function codeAddress() {
    var address = document.getElementById("formatedAddress").value;
    geocoder.geocode( { 'address': address}, function(results, status) {
        if (status == google.maps.GeocoderStatus.OK) {
            map.setCenter(results[0].geometry.location);
        }
    });
}


$(document).ready(function(){
    // Do stuff here, including _calling_ codeAddress(), but not _defining_ it!
});

You must write that function body outside the ready();

because ready is used to call a function or to bind a function with binding id like this.

$(document).ready(function() {
    $("Some id/class name").click(function(){
        alert("i'm in");
    });
});

but you can't do this if you are calling "showAmount" function onchange/onclick event

$(document).ready(function() {
    function showAmount(value){
        alert(value);
    }

});

You have to write "showAmount" outside the ready();

function showAmount(value){
    alert(value);//will be called on event it is bind with
}
$(document).ready(function() {
    alert("will display on page load")
});