A historical atlas is an atlas that includes historical maps and charts depicting the evolving geopolitical landscape. They are helpful in understanding historical context, the scope and scale of historical events and historical subjects (such as the expansion of the Roman Empire), and macro-history. Some historical atlases try to present the entire history of the world, such as the Historical Atlas of the World, while others are more specialised, for only one time period or location, such as the Historical Atlas of the American West or The Historical Atlas of China. They may also include historical photographs and explanatory text or essays.