<form action="sehirdetay.php" method="get">
<select name="plaka">
<option value="01">Adana</option>
<option value="02">Afyon</option>
....
<option value="81">Düzce</option>
</select>
<input type="submit" value="git" />
</form>
sehirday.php de şöyle olsun
<?php
if (isset($_GET["plaka]) &&...