Tip of the Month

Deriving Slope from DEM

Using the Spatial Analyst or 3D Analyst extensions one can derive slope from existing elevation data. Slope is the rate of maximum change in z-value from each cell.

1. Bring your elevation data into ArcMap.

File > Add Data > Navigate to your data source > Click Add

2. If your elevation data is in Geographic Coordinate System you must reproject it. When the slope function works it takes the rise over run. If your data is in Geographic it assumes the run is metric when it is really degrees.

In ArcToolbox go to Data Management Tools > Projections and Transformations > Raster > Reproject Raster

3. Now that your data in projected you can using the Slope Function. There are 3 ways to access this function:
A. Spatial Analyst Extension

Turn on the Spatial Anayst Extension under View > Toolbars

On the toolbars menu go to Spatial Analyst > Surface Analysis > Slope

Have your input elevation dataset be the projected elevation

Select if you want your output in Degrees or Percent

Specify an output Cell Size

Specify an output slope dataset

Click Ok

B. Spatial Analyst Extension Raster Calculator

Turn on the Spatial Anayst Extension under View > Toolbars

On the toolbars menu go to Spatial Analyst > Raster Calculator

Type in SLOPE(<our elevation data> )

Click Run

C. 3-D Analyst Extension

Turn on the Spatial Anayst Extension under View > Toolbars

On the toolbars menu go to 3-D > Surface Analysis > Slope

Have your input elevation dataset be the projected elevation

Select if you want your output in Degrees or Percent

Specify an output Cell Size

Specify an output slope dataset

Click Ok

View Other Tips

Saving Data From ArcMap as KML.