http://viewer.nationalmap.gov/launch/
http://eros.usgs.gov/elevation-products
http://nationalmap.gov/elevation.html
http://www.usgs.gov/
http://data.usgs.gov/datacatalog/#fq=dataType%3A(collection%20OR%20non-collection)&q=*%3A*
原文：http://www.cnblogs.com/lovebay/p/5106606.html