on that german page [login to view URL] you can search "ZIPCode or City".
And it have autocomplete for all cities. I need whole Germany.
a client will create a product with zipcode 10001
now someone who search a product in that region can search zip 10001 and border arround +20km for example
Then summary shows all results of zip code 10001 and arround 20km.
Maybe 10001 | 10002 | 10003 | ...
Think you need use a plugin like openstreetmap.