topic Re: Questions about USGS NED Data in 3D Questions

Questions about USGS NED Data

GregSullivan1 — Fri, 26 Jul 2013 12:53:28 GMT

Hello,

I am working with USGS NED 1/9 Arc Second Data and I am attemping a few different things that I am having trouble with.
Is there anyway to figure out what resolution the data is because I want to use the flow accumulation command to show cells with a certain acreage flowing to it but I cannot figure out how to do this because I do not know the size of the cells.
Also, is there anyway to create a point file from the NED data to see where the points were actually shot?
And one last one, what is the difference between the ArcGrid format and the GridFloat format?

Re: Questions about USGS NED Data

JimCousins — Mon, 29 Jul 2013 12:44:17 GMT

Hello, Greg.
Resolution: You can always right click a layer, go to Properties>>Source. 3rd entry is the Cell Size. (1/9th arc second data is approx. 3 meters)
See where the points were collected: No. The NED is an interpolation result. You would need the original dataset to see actual collection locations.
ArcGrid vs GridFloat: ArcGrid is an integer grid, whereas GridFloat is a floating point grid. Basically no decimal places vs decimal places.(float also can store a larger number).
Regards,
Jim

Re: Questions about USGS NED Data

JeffreySwain — Mon, 05 Aug 2013 11:23:48 GMT

Esri GRIDs are 32 bit float by default. I am unsure what an ArcGrid is, but if you mean Esri GRID raster or an extensionless raster then it should be float already. I would be sure to project your data from WGS 1984 if you desire to use the NED files directly. Be sure that you have the elevations in meters and then choose a coordinate system based on meters. That will make your calculations come out correctly.

Re: Questions about USGS NED Data

AlmaA — Sun, 13 Dec 2020 02:16:22 GMT

Hi! thanks for this useful info... does arc second mean the units are also in meters? I am working with a USGS NED 1/3 arc second DEM. I know this means approx. 10 meters, but do I have to convert the units to meters? I want to merge it with another DEM that is in meters. thanks!