Mapfile Extent

[Oliver Ishmael]

Dear all,

I'm still a bit of a noob to all this, but have the following problem:

I am trying modify the Gmap demo to form a template i can work with.
Currently it views a .tif (USA) and i would like it to view a .tif (UK) with
additional associated layers.

How do i work out the extents of my new layer (UK .tif)?

..and ensure that i do not just see a dot at the centre of the screen which
requires me to multi-zoom before it is visible and informative?
(min manx-scale - how do i know??)

Any help and suggestions greatly appreciated

Olly