Could this possibly be the new Red Dead Redemption 2 map? This could be proof it is.
This Red Dead Redemption 2 map leaked a few days ago on websites such reddit.com, 4chan.org and more. Users have analysed the image, mainly to the old map and the details of the locations. One reddit user mentioned the location of one of the areas, namely to another take2 game soon to be released in October 2016, Mafia 3, more about Mafia 3 in the suggested articles at the bottom. The location being New Bordeaux, these games both share this location so it may hint there may be some sort of Easter egg(s) throughout the game, could the recent announcement of Mafia 3, mean an announcement of Red Dead Redemption 2 coming soon, perhaps at E3, who knows currently.
The reference of the same location, this could possibly mean that this is real, more proof that it could possibly be real is the general location names, they are similar, for example Cumberland Forest and Cholla Springs, also the inclusion of the Grizzlies is exciting for most people. Members of online forum NeoGaf have also mentioned new information, for example:
A source close to the development of the new Red Dead game has now confirmed to us that the map is indeed the real deal, revealing that this is a “very recent” art direction map for the upcoming title.
They also confirmed that the game will be set before the events of Redemption, and that the new map is just east of the one that featured in Red Dead Redemption.
That is more confirmation, the final piece of proof is that there is no presence of any sort of railroad, on the Red Dead Redemption 2 leaked map, meaning a lack of train travel, combat etc. This also means that the game must be set earlier than Red Dead Redemption, since Red Dead Redemption had a strong railroad or train network.