USGS National Map Example

The USGS National Map provides topographic information for the USA. Users may search, map, and download data products.

Data Credit: USGS

Grand Canyon

1.) Open the USGS National Map Viewer.

2.) Under the Datasets tab select Elevation Products, then 1/3 arc-second DEM and IMG file format. Next, select Imagery - 1 meter (NAIP).

3.) Go to the map and type in "Grand Canyon National Park" next to Address/Place and press Go.

4.) Adjust the map so it covers the area that you want and select Use Map and Current Extent.

5.) Select Find Products and a results link should appear for each type of product in the Products tab.

6.) Select results and download each file. For large numbers of files, you can download a list of URLs (.CSV format) and create a download script (using the curl command, for example).

7.) Unzip the elevation files and mosaic multiple files together (if more than one).

gdalwarp imgn36w112_13.img imgn36w113_13.img imgn37w112_13.img imgn37w113_13.img dem.tif

8.) Remove the alpha band from the orthoimage files.

gdal_translate -mo "AREA_OR_POINT=Point" -b 1 -b 2 -b 3 m_3511101_ne_12_1_20130607_20130819.jp2 m_3511101_ne_12_1_20130607_20130819.tif

9.) Mosaic multiple orthoimage files together into ortho.tif.

10.) Run gdalinfo and copy and paste the projection into ortho.prj. The file should contain the following:

PROJCS["WGS_1984_Web_Mercator_Auxiliary_Sphere",
    GEOGCS["GCS_WGS_1984",
        DATUM["D_WGS_1984",
            SPHEROID["WGS_1984",6378137.0,298.257223563]],
        PRIMEM["Greenwich",0.0],
        UNIT["Degree",0.017453292519943295]],
    PROJECTION["Mercator_Auxiliary_Sphere"],
    PARAMETER["False_Easting",0.0],
    PARAMETER["False_Northing",0.0],
    PARAMETER["Central_Meridian",0.0],
    PARAMETER["Standard_Parallel_1",0.0],
    PARAMETER["Auxiliary_Sphere_Type",0.0],
    UNIT["Meter",1.0],
    EXTENSION["PROJ4","+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs"]]

11.) Project the DEM with the orthoimage projection.

gdalwarp -t_srs ortho.prj -r bilinear dem.tif proj_dem.tif

12.) Change pixel size of DEM to 8 meters.

gdalwarp -tr 8.0 8.0 -r bilinear proj_dem.tif proj_dem_8.tif

13.) Crop the DEM to the same physical area as the orthoimage.

gdal_translate -strict -projwin -12509530.981 4343709.909 -12453864.981 4292020.909 proj_dem_8.tif proj_dem_8_cropped.tif

14.) Create a landscape directory called GrandCanyon and then create the layers.

layerfactory -file=proj_dem_8_cropped.tif -landscape=GrandCanyon -type=elevation -tilesize=64
layerfactory -file=ortho.tif -landscape=GrandCanyon -type=colorimage -tilesize=512

15.) View the landscape in DERT