topic z-factor in ArcGIS Spatial Analyst Questions

z-factor

DanielRockefeller1 — Tue, 06 Aug 2013 13:45:50 GMT

Hi,

I'm relatively new to GIS and I'm attempting to calculate the slope from a DEM raster of the Adirondack Park.

<Spatial_Reference>NAD_1983_UTM_Zone_18N
<Linear_Unit>Meter (1.000000)</Linear_Unit>
<Angular_Unit>Degree (0.017453292519943295)

I'm having trouble understanding how to determine if I need to change the z-factor from the default "1" and then which z-factor to use if one is needed.

Can anyone lend a hand?

Re: z-factor

Luke_Pinner — Tue, 06 Aug 2013 21:21:23 GMT

Your linear units (XY) are metres. You do not need to change the Z factor as your elevation values should also be in metres. If for some reason your elevation values are in feet, you would use a z-factor of 0.3048 to convert your elevation from feet to meters (1 foot = 0.3048 meters).

Ignore below (It's only relevant if your linear units are in degrees).

See this thread: Z factor in slope tool and these articles: Setting the Z Factor parameter correctly and Determining a Z-factor for scaling linear elevation units to match geographic coordinate values.

Re: z-factor

NoahHuntington — Thu, 09 Jan 2014 13:10:49 GMT

Your linear units (XY) are metres. You do not need to change the Z factor as your elevation values should also be in metres. If for some reason your elevation values are in feet, you would use a z-factor of 0.3048 to convert your elevation from feet to meters (1 foot = 0.3048 meters).

Ignore below (It's only relevant if your linear units are in degrees).

See this thread: Z factor in slope tool and these articles: Setting the Z Factor parameter correctly and Determining a Z-factor for scaling linear elevation units to match geographic coordinate values.

If my x y units are feet do I use the inverse for a z factor of 3.2808?

Re: z-factor

Luke_Pinner — Fri, 10 Jan 2014 02:55:17 GMT

If your Z units are in metres, then yes - http://resources.arcgis.com/en/help/main/10.1/index.html#//009t00000056000000