Map of the west coast of north america from just below the 42nd parallel to just above the 54,40 line. the map shows mexico controlling the territory below the 42nd parallel. it shows the location of the oregon country between the 42nd parallel and the 54,40 line, the location of the 49th parallel running through the middle of the oregon country, british north america to the east of the oregon country and above the 49th parallel, and the united states to the east of the oregon country between the 49th parallel and the 42nd parallel. © roke 2006 creative commons, attribution-share alike 3.0 how did this map change following the treaty of washington in 1846? the oregon country was divided between britain and the united states at the 49th parallel. the oregon country was split into the washington and oregon territories using the 49th parallel as the new boundary. the boundary between the oregon country and mexico was shifted from the 42nd parallel to the oregon trail route. the portion of the oregon country below the 49th parallel became part of mexico, while the portion above the 49th parallel became part of great britain.