add_action( 'manage_colourmedia_column', 'colourmedia_columns', 10, 2 );

function manage_colourmedia_columns( $column, $post_id ) {
	global $post;
        $terms = get_post_meta( $post_id );
	switch( $column ) {

		case 'thumbnail' :
	               $url = get_the_post_thumbnail_url($post_id);
			printf( '<img src="'.$url.'" style="width:100px"/>' );
                      break;
		case 'city' :
			printf($terms['City'][0]);
			break;
		case 'category' :
		 $cat_list = wp_get_post_terms($post->ID, 'category', array("fields" => "names"));
		foreach($cat_list as &$category){
			echo '<a href="'. site_url().'/wp-admin/edit.php?post_type=CUSTOMPOSTTYPE&category_name='.$category.'"/>'.$category.'</a>, ';
		                           }
		break;
		
		case 'featured' :
			printf($terms["Featured"][0]);
		
		break;
			
		/* Just break out of the switch statement for everything else. */
		default :
			break;
	}
}