topic How do I symbolize / get elevation data from DEM10 or DEM10i layer? in Mapping Questions

How do I symbolize / get elevation data from DEM10 or DEM10i layer?

RobinHolcomb — Mon, 30 Mar 2015 21:02:01 GMT

I am interested in characterizing vegetation along a reservoir and need elevation data that is pretty precise - idealy 1-2 foot contours. I have access to a DEM10 and DEM 10i raster layer. I would like to break up the different elevations and symbolize them differently. When I use the Identify tool at the top of the screen it gives me elevations for points that I know are not that accurate.

Re: How do I symbolize / get elevation data from DEM10 or DEM10i layer?

IanMurray — Mon, 30 Mar 2015 21:06:31 GMT

Make sure you know what units the raster are in, generally they are in meters, not feet for elevation. What is the source of your DEM data and what sort of resolution is it?

Re: How do I symbolize / get elevation data from DEM10 or DEM10i layer?

RobinHolcomb — Mon, 30 Mar 2015 22:02:22 GMT

Thank you Ian

I am looking under layer properties of my DEM 10i layer and it says that its source is from USGS NED 10m DEM10 and that it was then converted to feet so I guess that it would be in feet.

The following paragraph in quotes talks about resolution. The area in question is in Washington state I would guess that the resolution is either 1 arc/second or 1/3 arc-second.

" NED data are available nationally at resolutions of 1 arc-second (approx. 30 meters) and 1/3 arc-second (approx. 10 meters), and in limited areas at 1/9 arc-second (approx. 3 meters). At present, the bulk of Alaska is only available at a 2 arc-second (approx. 60 meters) resolution, owing to a paucity of higher resolution source data, though some areas are available at resolutions of 1 and 1/3 arc-second with plans for significant upgrades of the state over the next five years. The NED is updated on a nominal two month cycle to integrate newly available, improved elevation source data."

Re: How do I symbolize / get elevation data from DEM10 or DEM10i layer?

IanMurray — Mon, 30 Mar 2015 22:20:31 GMT

If you are needing 1-2 foot contours, then you would be needing a much higher resolution elevation data then what is available from the NED. Even if you have the 1/3 arc-second data(which it sounds like you do), that means each cell is 10m x 10m and you get the average elevation for that 10m x 10m. While you can generate contours from this at 1-2 feet, generally speaking the elevation data isn't fine enough for it to be accurate at all or true to the actual surface. For 1-2 foot contours, you would need likely 1m resolution DEM, which would likely only be available where LiDAR has been flown. You can check the United States Interagency Elevation Inventory(USIEI) hosted by NOAA to see if your area could have LiDAR derived data.

Where is your Area of Interest, and how large of an area are you looking at? Also could you provide the link you used to download the data(I'm guessing it was a ftp connection through either NRCS or USGS Earth Explorer or something similar)?

Re: How do I symbolize / get elevation data from DEM10 or DEM10i layer?

RobinHolcomb — Mon, 30 Mar 2015 23:00:13 GMT

Thanks again, Ian. -- much great information which I will pursue. My area of interest is actually 2 areas of shoreline on Lake Cle Elum which is a reservoir right in the middle of the state off washington. I am intersted in looking at an area of about 3 acres on one part of the lake and an area of about 10 acres on the north part of the lake. I got the DEM layers from a gis layer database that my state agency has -- I am pretty sure that they got it from USGS