Map display

[Paul Frost]

There are dozens of these javascript plugins out there, some free and some with a charge.
mlens is one example that you could install on any website (if you know how).

But there are some user implications that need to think about.
It requires a very high resolution image to be of any use, and if the visitor to your page is on a data restricted device (either cost or speed), like a tablet, phone or dongle they may not be happy to have downloaded a large image if they didn't particularly need or want it.
Plus if it's a touch screen, your finger will probably obscure the magnifying glass and so not be much use; a separate slider control can be better in this case.
But most touch screen devices have a pinch to zoom feature anyway so don't need any extra scripts.

I think the best and most user friendly way is to just have a link to a high resolution version of the map/image and let them decide if they want it.

[Jethro]

What I liked about this system was the ability to look at the whole map and get an appreciation of the shape of the course and the route choice options particularly on longer legs while at the same time being able to zoom in on the fine detail, particularly around controls.