Show data like tool tip when hovered over portion or regions on a custom map
What kind of map is it? An HTML imagemap (using  and  tags)? If so, you can use the EasyToolTip and MapHilight JavaScript libraries. They aren't connected to any Drupal modules, as far as I know.

EasyToolTip allows you to format the tooltips almost any way you want, and MapHilight allows you to highlight the section of a map that the mouse is hovering over.