Land Area and Persons Per Square Mile - This resource links to Census Tables that include Land Area and Persons Per Square Mile (Population density). While the different geographies must be viewed separately, data is available at the national, state, parish, and city level. Note that availability of city level data will depend upon whether it is included in the Census.
The National Map - This resource gives various geographical information, including topography and hydrology. A portal with a slightly different interface can be found here. Note that due to the size of the resource, it may take some time for data sets to load.
Topographic Map Symbols - This resource offers guidance on how to read topographical maps. Since topographical maps are frequently used to show key information about geography, including elevation, it may be useful to have as a reference.
USGS Map Locator - This searchable resource helps with locating any maps on a given area, such as topographical maps. Note that due to the size of the resource, it may take some time to load.