url string changes

Hi there

I’m listing taxonomies in a dropdown on a taxonomy template using this code :

<?php
function get_terms_dropdown($taxonomies, $args){
	$myterms = get_terms($taxonomies, $args);
	$output ="<select name='area'>";
	foreach($myterms as $term){
		$root_url = get_bloginfo('url');
		$term_taxonomy=$term->taxonomy;
		$term_slug=$term->slug;
		$term_name =$term->name;
		$link = $term_slug;
		$output .="<option value='".$link."'>".$term_name."</option>";
	}
	$output .="</select>";
return $output;
}
?>
<form action="<?php bloginfo('url'); ?>" method="get">
<?php
$taxonomies = array('area');
$args = array('orderby'=>'name','hide_empty'=>false);
$select = get_terms_dropdown($taxonomies, $args);
echo $select;
?>
<input type="submit" value="View" />
</form>

Works fine but when I add a variable to the link:
$link = $term_slug.'/?id=map';
it adds it fine to the html output but on submit alters the url from :

mysite.com/area/north-central/

to

mysite.com/?area=south-central%2F%3Fid%3Dmap

Which throws up a 404.

Any pointers please?