jQuery select change show/hide div event

Use following JQuery. Demo

$(function() {
    $('#row_dim').hide(); 
    $('#type').change(function(){
        if($('#type').val() == 'parcel') {
            $('#row_dim').show(); 
        } else {
            $('#row_dim').hide(); 
        } 
    });
});

Try:

if($("option[value='parcel']").is(":checked"))
   $('#row_dim').show();

Or even:

$(function() {
    $('#type').change(function(){
        $('#row_dim')[ ($("option[value='parcel']").is(":checked"))? "show" : "hide" ]();  
    });
});

JSFiddle: http://jsfiddle.net/3w5kD/

change your jquery method to

$(function () { /* DOM ready */
    $("#type").change(function () {
        alert('The option with value ' + $(this).val());
        //hide the element you want to hide here with
        //("id").attr("display","block"); // to show
        //("id").attr("display","none"); // to hide
    });
});