How to Explore NorthEast (Out of Map) in Red Dead Redemption 2 ? 

Step 1

First, you need to go to this location.

Step 2

And then camp there.

Step 3

You have to mark map with this location.

Step 4

And go north towards the marker.

Step 5

Look at the ground and follow the route.

Step 6

When the route goes down, you will need to exit the horse.

Step 7

After that, go east and slide down the mountain.

Step 8

When here, you have to mark the spot outside map border.

Step 9

Go to the marker outside map border.

Step 10

When outside the border, you need to mark the top right point.

Step 11

Go east towards the marker.

Step 12

You may need to navigate some cliffs here.

Step 13

And continue to north east corner of the map.

Step 14

You will find a river and you may sink a bit.

Step 15

This is the Kamassa River (follow it north).

Step 16

This is the source of Kamassa River in the game.

Step 17

Keep going towards the north east marker.

Step 18

This rock is north east map cursor limit.

Step 19

You can keep going east (make SE mark)

Step 20

After that, you have to go southeast past map boundary.

Step 21

Here is a nice view showing the water border.

Step 22

Continue until we hit water border.

Step 23

This is the farthest east you can go.

Step 24

You have to follow the water border.

Step 25

What happens if you enter water?

Step 26

You will die.