I'm amusing myself a bit by tracing the river that flows through my home town. I just did a stretch of 20km from the nearest city upstream and now I'm getting ready to do the same 20km downstream, where it merges with another river.

Is it OK to do this by using the photographic material from Yahoo? I don't see anybody who is going to use a kayak to trace the flow of a river like this, risking an expensive GPS unit.

Polyglot