Andrew Graham, a HBC trader at Fort York, collected geographical information from Indians and from company traders who wintered inland. This map, a composite of two of Graham's, draws particularly on William Tomison, who journeyed up the Severn River and across Lakes Winnipeg (Frenchman's Lake or Little Sea) to reach the grasslands in the Assiniboine valley; and on Matthew Cocking, who explored upstream from the forks of the Saskatchewan River and south through Eagle Hills.