NED stands for National Elevation Dataset and is a new form of digital evelation model available in several different levels. This site is designed to show the differences between DTED, SRTM, and NED. Every image on this page links to a larger version.
This site is a companion to my SRTM and DTED Information site.
WARNING - After viewing this site, you will probably want to toss out your existing data and buy a bigger hard drive!
The NED data is currently only available from the USGS Seamless Data Distribution System. Please let me know if it ever shows up on an FTP site. The NED data available there is NED-2-Arcsecond (60 meter - Alaska only), NED-1-Arcsecond (30 meter), NED-1/3-Arcsecond (10 meter), and NED-1/9-Arcsecond (3 meter). There is also a lot of other data available through that site however that is beyond the scope of this page.
These are trimmed from screen captures of the Seamless site. I changed the background color to make the details stand out a bit better. They show what areas are covered by each type of NED data.
Alaska and Hawaii are not shown as having any coverage in the NED-1-Arcsecond data.
Even though this shows coverage in Hawaii, if you zoom in on Hawaii, there is no NED data shown at all.
This is currently the only area covered with this data.
In building this site, I wanted to show the differences between all the different types of data. Since the NED-1/9 only covers a very limited area, I started by finding an interesting terrain feature that was covered by that data and would also be covered by all the other data types I wanted to compare. Since the NED-1/9 currently only covers portions of the state of Washington. The obvious choice for an interesting terrain feature in that area is Mount Saint Helens.
All these images were created using Radio Mobile. The images displayed on this page are one third the size of the original TIFF versions. I scaled them and saved them as jpg with The GIMP.
The NED data was supplied in zip files containing world files, projection files, and other related things as well as metadata files. The metadata files contain interesting information on the background of the data. The NED-1/9 metadata file is very interesting and describes how the data was acquired using LIDAR and GPS and even gives the tail number of the aircraft used. The stated accuracy of the NED-1/9 data is 30 centimeters horizontally and 15 centimeters vertically!
The NED files are not small. The area I downloaded is roughly 0.2 degrees north to south and 0.25 degrees east to west. I downloaded the exact same area in all three NED data types. Seamless assigns random numbers to the download files. Here they are as I received them:
Mount Saint Helens - SRTM-30
Mount Saint Helens - DTED-0
Mount Saint Helens - DTED-1
Mount Saint Helens - SRTM-3
Mount Saint Helens - SRTM-1
Mount Saint Helens - NED-1
Mount Saint Helens - NED-1/3
Mount Saint Helens - NED-1/9