add_action('show_user_profile', 'addCityField');
add_action('personal_options_update','updateCityField');

// show input field for city information on the user's profile page
function addCityField() {
	global $user_ID;
	$legend = 'Location';
	$group = 'field_group';

	$prefix_html = " <fieldset><legend>$legend</legend>";
	$postfix_html = '</fieldset>';
	$body_html = '';

	$body_html .="<p><label>City</label><br />";
	$body_html .= "<input type='text' name='city' value='" . get_usermeta($user_ID,'city') . "' />";
	$body_html .= "</p>\n";

 	echo $prefix_html.$body_html.$postfix_html;

}
// if user makes changes to city field on his profile page, save the changes
function updateCityField() {
	global $user_ID;
	$city 	 = $_POST["city"];
	update_usermeta($user_ID,"city", $city);

}