How do I change the size of Google Maps in details view.

The size of Google Maps in a listing details view are defined in this template file:

/components/com_mtree/templates/banyan/sub_map.tpl.php in line 3 - 4:

    $width = '100%';
    $height = '300px';

Changing the value of the width and height will resize the Google Maps in listing details view.