http://www.theverge.com/2015/4/3/8341197/united-states-map-every-road?utm_campaign=theverge&utm_content=feature&utm_medium=social&utm_source=twitter
https://cdn3.vox-cdn.com/thumbor/8oEYT-6B-bwn3KQEECQryuMcRnM=/0x0:13500x9000/1025x683/cdn0.vox-cdn.com/uploads/chorus_image/image/46041370/USA.0.0.png
中西部には山がないことが判明