Here, (via The Dish) an interesting interactive article by Anne Kelly Knowles, from The Smithsonian, showing what commanders could and couldn't see during crucial points during the Battle of Gettysburg. It's really fun, and well worth a look.
We're used to seeing God's-eye-views of battlefield diagrams which show everything, and also know how things worked out, so we get a skewed sense of what it was like then.
The article shows panoramas, which lets you scan across a generated image of what the battlefield actually looked like from a commander's point of view. Of course, it is devoid of concealing smoke and mist, as well as time pressure, noise of detonations, and constant influx of frantic written and spoken messages.
In addition, you can examine viewsheds, which show the map with blind areas from the commander's point of view. You can see how at crucial points, Lee had no way to see significant parts of the Union force. Of course, he did not need to rely solely on his own eyesight: he got those aforementioned frantic messages.
Still, walking through the battle using this tool gives you a real sense of the blindness that was inherent to the technological level at which any of these battles were fought. You just couldn't see anything. How did the best commanders integrate all the information thay had into a simulation of what they concluded was out there? It's an interesting form of mental processing, and clearly only a few of them were really good at it.