PHP URLstring dropdown

<?php
if($_POST['submit']) {
$URLstring = '/tag/' . $_POST['type'] . '+' . $_POST['age'] . '+' . $_POST['gender'] . '+' . $_POST['location'] . '/';
header("Location: " . $URLstring);
}
?>

<form action="<?php echo $URLstring ?>" method="post" name="form1">
<div>
<select name="type">
    <option value="">Any</option>
    <option value="dog">Dog</option>
    <option value="cat">Cat</option>
    <option value="other">Other</option>
</select>
<select name="age">
    <option value="">Any</option>
    <option value="0to12months">0 - 12 months</option>
    <option value="1to3years">1 - 3 years</option>
    <option value="4to8years">4 - 8 years</option>
    <option value="8plusyears">8+ years</option>
</select>
<select name="gender">
    <option value="">Any</option>
    <option value="male">Male</option>
    <option value="female">Female</option>
</select>
<select name="location">
    <option value="NorthWest">North West</option>
    <option value="yorkshireandhumber">Yorkshire &amp; Humber</option>
    <option value="#NE">North East (England)</option>
    <option value="#NW">North West (England)</option>
    <option value="#CE">Central (England)</option>
    <option value="#SW">South East (England)</option>
    <option value="#SW">South West (England)</option>
    <option value="#Ireland">Ireland</option>
    <option value="#Scotland">Scotland</option>
    <option value="#Wales">Wales</option>
</select>
<button type="submit" name="submit" value="sent">submit</button>
</div>