I have a map, and I want to overlay an image in such a way that I can fade the image from clear to opaque and back at will (like some weather sites do with radar information etc)

I started off thinking I needed to look at how the Z index can be messed with, but now I think I may be up the wrong creek.

Anyone care to point in the right direction?

Is this for a display, or going somewhere you won't have the convenience of having the thing in front of you to twiddle? 'Cos Photoshop'll let you do that.

Ideally I'd like it on a webpage, though it's just for family
Photoshop would do at a pinch though, thanks

jquery fadeIn() and fadeOut() ? also you can animate the css opacity attribute.

thanks, I'll have a look

Are you wanting visitors to be able to do it in real time with a slider?  Or is it a cycling slideshow effect?

real time with a slider would be perfect.