The National Mall in DC has the deception effect that Las Vegas Strip has, just in a smaller scale. In the open area of and near the Mall, every landmark seems walkable. On a nice day with plenty of time, walking is indeed the best way to get around. But under the heat in the muggy August or when you are in a rush, getting from the Lincoln Memorial to the visitor center of the Capitol on foot would not be quite feasible. Tidal Basin is the same. It actually takes some time to walk around the basin. If lighting and timing are important to you, you might want to know exactly where and when to be to get good pictures.
華府的國家廣場(the Mall)跟拉斯維加斯一樣有騙人效果，什麼都看起來很近但其實要走很久，DC當然不像拉斯維加斯大道一棟飯店就是一公里半這麼誇張，大部分景點也真的都走得到，但熱死人的夏天或者趕時間的時候，真的不會想要從林肯紀念堂走到國會山莊。潮汐湖(Tidal Basin)也是一樣的道理，如果要拍照、要追求某個時間點或特定的光線，真的很需要知道該在什麼時候去哪。