It is preferable that the new road traverses less steep slopes. You will reclassify the slope layer, slicing the values into equal intervals. You’ll assign a value of 10 to the most costly slopes (those with the steepest angle of slope), 1 to the least costly slopes (those with the least angle of slope), and rank the values in between linearly.

To do so, expand the Reclass toolset in the Spatial Analyst Tools toolbox, and click and drag the Reclassify tool onto the ModelBuilder window. Right-click the Reclassify tool element and click Open. Click the Input raster drop-down arrow and click the Slope output variable. Accept the default for the Reclass field parameter so the Value field will be used. Click Classify. Click the Method drop-down arrow and click Equal Interval. Click the Classes drop-down arrow and click 10. Click OK.

You want to avoid steep slopes when constructing the road, so steep slopes should be assigned higher values in the cost dataset. Because the default assigns higher values to steeper slopes, you do not need to change the default New Values.

Accept the default location for the value of the Output raster parameter, but type “Rslope_ex3” for the name, and Click OK.

Click the Auto Layout button, then click the Full Extent button to apply the current diagram properties to the elements and place them within the display window. Right-click the derived data element for the Reclassify tool and click Rename. Type “Reclassed slope” and click OK. Right-click the Reclassed slope derived data element and click Add To Display.

Right-click the Reclassify tool element and click Run to run the process.

Examine the reclassed slope layer added to your ArcMap display. It shows locations that are costlier than others for constructing a road—higher values indicate the costlier areas that should be avoided.