exclude or include markers based on content?

Hi,
First off, this is an amazing plugin – so user friendly and simple to implement. Thank you!

I’m using it to display a map with all the timber yards in the UK. I’d love to be able to call a version of the map that displays only markers that contain a certain string, or have a certain value in one of the marker fields.

Is there a way to do this?

So for example either by calling the page with a url parameter, or a parameter in the shortcode?

Thanks,
Ben.

The page I need help with: [log in to see the link]