Filter on custom field

Hello,
i am french, i tried to write in english 🙂

Here is my problem :
I use nearby map on a website and i added a custom field named “Departement” in the posts “Place”. I would like to have a filter (with a select or text-field) on the page Map for this custom-field (for example I choose the department 06 to display on the page places located in this department).

I hope I was clear in my explanations 🙂

Thank you in advance for your help
Eric

http://wordpress.org/plugins/nearby-map/