Guide: Analyzing Terrain for Vineyard Sites in ArcGIS Desktop

In this guide, you’ll generate raster data to pinpoint potential vineyard locations around San Diego, California, using ArcGIS Desktop 10.7 with the Spatial Analyst extension. The sites must meet these conditions:

• Elevation above 200 meters (656 feet)
• Slope between 1.5% and 15%
• South-facing exposure (southeast, south, or southwest)

You’ll create slope and aspect layers from an elevation surface and use them to perform a preliminary suitability analysis.

Time Required: About 50 minutes
Requirements:

• ArcGIS Desktop 10.7 (Basic, Standard, or Advanced)
• Spatial Analyst extension

Step 1: Obtain the Data

1. Download the dataset if you haven’t already.
2. Save it to a folder like C:\Training\TerrainData.

Step 2: Explore the Elevation Surface

1. Open ArcMap and load C:\Training\TerrainData\AnalysisMap.mxd.
   • The map includes a basemap (e.g., USA Topo Maps) showing San Diego.
2. Activate the Spatial Analyst extension:
   • Go to Customize > Toolbars > Extensions.
   • Check Spatial Analyst and click Close.
3. In the Catalog window, expand the SanDiegoData.gdb geodatabase and add the sd_elevation layer to the map.
4. Enable the Effects toolbar:
   • From Customize > Toolbars, turn on Effects.
   • Set the layer to sd_elevation.
   • Click the Transparency button and slide to 40% to see the basemap beneath.
5. Zoom to the Montgomery Field bookmark (via Bookmarks menu).
   • The basemap shows the airstrip at ~415 feet. Use the Identify tool to check the raster’s elevation value here.
   • Compare to determine the raster’s vertical units (e.g., meters if ~126, feet if ~415).
6. Check the raster’s horizontal resolution:
   • Right-click sd_elevation, open Properties, and go to the Source tab.
   • Note the cell size and its units (e.g., meters).

Insight:

• Knowing the units ensures accurate slope calculations later.

Step 3: Configure Analysis Settings

1. From the Geoprocessing menu, select Environments.
2. Set:
   • Processing Extent: Match the sd_elevation layer.
   • Raster Analysis: Cell size to match sd_elevation.
   • (Pre-set: Workspace at C:\Training\TerrainData\SanDiegoData.gdb, Scratch at C:\Training\TerrainData\Output.gdb, Coordinates as input.)
3. Click OK.

Step 4: Create a Slope Surface

1. Search for and open the Slope (Spatial Analyst) tool.
2. Configure:
   • Input Raster: sd_elevation
   • Output Raster: C:\Training\TerrainData\Output.gdb\SlopeSurface
   • Output Measurement: PERCENT_RISE (matches the 1.5–15% criteria).
   • Z Factor: 3.2808 (converts feet to meters if vertical units are feet and horizontal are meters—adjust based on Step 2 findings).
3. Click OK.
4. Set SlopeSurface transparency to 25% via the Effects toolbar.
5. Turn off the sd_elevation layer and save the map.
6. Zoom to the Cockatoo Grove bookmark.
   • Notice edge cells are less steep (lighter) than interior ones—likely due to fewer neighbors affecting edge calculations.

Insight:

• Slope ranges from 0 to over 100%, with red indicating steeper areas.

Step 5: Create an Aspect Surface

1. Search for and open the Aspect (Spatial Analyst) tool.
2. Set:
   • Input Raster: sd_elevation
   • Output Raster: C:\Training\TerrainData\Output.gdb\AspectSurface
3. Click OK.
4. Open AspectSurface Properties, set Display transparency to 40%, and click OK.
5. Turn off SlopeSurface and save the map.
6. Zoom to the North Island bookmark.
   • Note banding from the 1-meter vertical resolution of sd_elevation—higher resolution (e.g., 0.1 meters) would reduce this.
7. Return to full extent.

Insight:

• Aspect shows slope direction in degrees (0–360), with colors distinguishing orientations.

Step 6: Conduct a Binary Suitability Analysis

1. Search for and open the Raster Calculator (Spatial Analyst) tool.
2. Build this expression: ("Elevation" > 200) & ("SlopeSurface" >= 1.5) & ("SlopeSurface" <= 15) & (("AspectSurface" >= 90) & ("AspectSurface" <= 270))

• Double-click layers from the list, use operators (e.g., >, &), and type values.
• Elevation > 200 meters.
• Slope between 1.5% and 15%.
• Aspect 90°–270° (southeast to southwest, covering south).

3. Set:

• Output Raster: C:\Training\TerrainData\Output.gdb\VineyardSites

4. Click OK.
5. Check the result:

• Values of 1 (e.g., red areas) meet all criteria; 0 means unsuitable.
• North of La Mesa, identify a mountain with suitable southeast slopes.

Insight:

• Binary analysis outputs a yes/no map—1 for suitable, 0 for not—simplifying site selection.

Wrap-Up

1. Save the map in C:\Training\TerrainData\Output.
2. Close ArcMap.

Key Takeaways

• Why adjust the Z Factor?
• It aligns vertical and horizontal units for accurate slope computation.
• What’s binary suitability?
• A method to filter areas meeting all criteria (1) vs. those that don’t (0).
• Why do edges differ in slope?
• Fewer neighboring cells at edges reduce calculated steepness.