Introduction

This procedure outlines steps needed to clip Digital Elevation Model data to isolate a specific study area. The resulting GRID file will illustrate the topography of the study area with greater clarity.

• Run ArcMap and add the DEM file to a new view.
• If promted to create pyramids for the DEM, click OK. Pyramids enable the file to redraw faster.

• Use the zoom tools to create an ideal view of the desired study area.

• If the Spatial Analyst dropdown menu is NOT visible, select Tools > Extensions and make sure Spatial Analyst has a check in the box beside the listing.
• Select View > Toolbars > Spatial Analyst.
• From the Spatial Analyst dropdown menu, select "Options". The Options dialogue box appears.

• From the General Tab, use the browse button to define a working directory where the clip results will be saved.
• From the Extent Tab, select "same as display"
• From the Cell Size Tab, select "minimum of inputs"

• To accept these options and return to the map window, click OK.

  Using the Raster Calculator

• Select Spatial Analyst > Raster Calculator...

  The Raster Calculator dialogue box appears.

• In the expression box at the bottom of the window enter the following text:

newfilename = [DEMfilename]

Where "newfilename" will be the name of the clipped DEM and "DEMfilename" is the same as the DEM layer listed in the layers box of the Raster Calculator. See image below for example.



• Click "Evaluate".

  The clipped DEM is added to the data view. Turn off the original DEM layer and zoom out a bit to see only the clipped DEM.

• To adjust the colour scheme, double click the new DEM layer. The Layer Properties dialogue box appears.
• Select the "Symbology" tab.
• From the "Colour Ramp" dropdown, choose a suitable colour scheme. The selection shown below is good for displaying elevation data.

• Click "OK". The resulting DEM should display colours similar to the image below.

  

  For additional digital procedures see http://www.brocku.ca/maplibrary/procedures/procedures.htm

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