Separate categories parents, childs and grandchilds in dropdowns

Question

I'm new to wordpress and PHP Im trying to build a site that the user can select a destination so I did this by creating categories (country) subcategories (state) sub sub category (city) and I want to split them into 3 dynamic drop down menus when you select country the state automatically populates according to the parents then the same with city, then it will do a search for destinations (posts) attached to the selections.

So far I have one dropdown working but is listing all (parent, children, grandchildren) categories and doing the search correctly. how can I split them?

<?php $thecategories = array(
        'show_option_all'    => '',
        'show_option_none'   => '',
        'orderby'            => 'ID', 
        'order'              => 'ASC',
        'show_count'         => 0,
        'hide_empty'         => 1, 
        'child_of'           => 0,
        'exclude'            => '',
        'echo'               => 1,
        'selected'           => 0,
        'hierarchical'       => 0, 
        'name'               => 'cat',
        'id'                 => '',
        'class'              => 'postform',
        'depth'              => 0,
        'tab_index'          => 0,
        'taxonomy'           => 'category',
        'hide_if_empty'      => false
    ); ?>

<form action="<?php bloginfo('url'); ?>" method="get">
  <?php wp_dropdown_categories( $thecategories ); ?>
  <input type="submit" name="submit" value="view" />
</form>

Answer 1

I found a solution for this in case someone else has this issue, there is a plugin that can help achieve this it is called Category Ajax Chain Selects http://wordpress.org/extend/plugins/category-ajax-chain-selects/