I've managed through repetition and memorization to lock down the order of battle from the entire 1st Corps through the 2nd Division of the 2nd Corps down to the regimental level. It's amazing how much you can absorb when you put your mind to it.
Recently (earlier this month), I was in Gettysburg and managed to find my way up to Neill Avenue (also called Lost Lane). There is a narrow goat path that leads from a dead end street, down to a stream bottom, and back up a steep hillside. The route to the area isn't marked anywhere that I am aware of, and it is not handicapped accessible. The trail is about 8-10' wide and is bordered by private property. This I know because the landowner managed to hang "No Trespassing" signs on just about every tree that bordered the trail. The area of Neill Avenue is the extreme right position of the Union Army at Gettysburg. Here are some pictures I took, enjoy.
This is the original marker for Neill Avenue, visible in the second picture on the right hand side.
The view from the beginning of Neill Avenue. Note that the property on either side is privately owned.
Neill Avenue is actually in a couple of parts along this ridge line. This area has a wire across either end, possibly to impede horse traffic as there were a lot of tracks in the area and on surrounding trails. A few hundred yards beyond this picture is a second area with monuments.
This is the monument to the 49th NY Infantry on the lower end of Neill Avenue, they were in the 6th Corps and assigned to this position on the 3rd of July, 1863.
This next monument I really took a shine to. I really like the "Union Shield" design of it with the 6th Corps insignia in the middle. This monument is to the 7th Maine Infantry who were also assigned here on July 3rd.
Looking downhill on the right hand side you can see the 7th Maine Monument, and close to center you can see the monument to the 49th New York.
A little further up Neill Avenue and to the left we find a monument to the 43rd New York Infantry, they were assigned here on the 2nd of July. They had an impressive battle history including the Peninsula Campaign, the 7 Day's Battle, Antietam, Fredericksburg, Gettysburg (obviously), Grant's Overland Campaign, Petersburg, and Appomattox (to name a few)
Just a few steps from the 43rd NY Monument is a marker for the 3rd Brigade, 2nd Division of the 6th Corps.
Looking back down at the first section of Neill Avenue you can see the 3rd Brigade marker and the 43rd NY Monument.
Nearing the end of Neill Avenue (the second part of it) we approach the monument to 61st Pennsylvania. They held the position of the extreme right of the Army of the Potomac at Gettysburg. After marching 37 miles, they arrived at Gettysburg on July 2, 1863 and were assigned to assist the 12th Corps, they were moved to this position on the morning of July 3rd.
Finally we reach the marker denoting the extreme right of the Army of the Potomac. The little stone marker on the right is a flank marker from the 61st Pennsylvania. You can tell where the Park Service property ends by the "No Trespassing" sign on the tree in the background. Maybe it's me, but if you own property in a historic area, shouldn't you be willing to accept that people are going to want to be there?