What does this mean "Straddling the ... river, ....." (etc.)
If you are a person, then "to straddle" means to have one leg on one side of something and the other leg on the other side. If you sit on top of a fence, and hang one leg over each side, you are "straddling the fence". If you are on a men's bicycle, then your legs "straddle the crossbar".
It can refer to inanimate objects too. Bridges "straddle" a river or a road, meaning that one end of the bridge is on one side, and the other end is on the other side.