Questions about USGS NED Data

[GregSullivan1]

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?

[JimCousins]

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

[AlmaA]

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!

[JeffreySwain]

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.