Explore the study area

When siting a wind farm and mitigating the possibly damaging effects on its surroundings, developers and planners have to consider a large number of factors, almost all of which are geographical in nature. This investigation, known as an Environmental Impact Assessment (EIA)[1], takes into account potential impacts on human beings, plants, and animals; soil, water, air, climate, and the landscape; material assets; and aesthetics. The EIA identifies measures that can be taken, if needed, to eliminate or reduce potential impacts, sometimes resulting in rejection of the development proposals.

One common part of an EIA is a visual impact analysis to determine the visual impacts to scenic resources. This is done by generating maps of the zones of theoretical visibility. Visibility analysis is especially applicable for wind farm assessments because wind turbines are often very tall structures that are visually conspicuous due to their reflective surfaces and obviously non-natural geometry that contrast strongly with natural landscapes. You can see this in the photo below of the Low Spinney Wind Farm in the English Midlands.

Low Spinney Wind Farm in English Midlands

You'll investigate the proposed wind farm site, which is in the District of Rugby and County of Warwickshire in the United Kingdom. You'll explore other wind farms in the area. You'll also look at two landmarks from which the views are important—a nearby village and its conservancy area and a local heritage site.

Open the map

The proposed site for the Swift Wind Farm is northeast of the small village of Churchover in "rolling arable and pastoral farmland with scattered, small villages and isolated dwellings and farmsteads."[2] The location has good wind speeds, is accessible by a number of major roads, and is near a suitable power grid connection.

To see the wind farm and its surrounding area, you will open a map that has been created for you.

  1. Go to the ArcGIS Online group, I Can See for Miles and Miles.

    This group contains one item—a web map titled Swift Wind Farm by Learn_ArcGIS.

  2. Click the thumbnail to open the web map.

    Swift Wind Farm thumbnail

    The map opens. Before you continue, you'll sign in.

  3. If necessary, in the upper right corner, click Sign In. Sign in using your ArcGIS organizational account.
    Note:

    If you don't have an organizational account, you can sign up for an ArcGIS free trial.

  4. At the top of the Details pane on the left, click the Content button.

    Show Contents of Map button

    The proposed Swift Wind Farm and its turbines are displayed on the Esri Topographic basemap, a reference layer that provides geographic context for the map.

    Swift Wind Farm web map

    The surrounding landscape is indeed low hills with pastures, farms, and scattered villages, as stated in the EIA. Isolated dwellings and farmsteads are distributed widely in the countryside.

    You'll change the basemap to show satellite imagery so you can more easily see the vegetation, barren land, and other landscape features.

  5. On the ribbon, click Basemap and choose Imagery with Labels.

    Imagery with Labels basemap

    The map updates to show a satellite image.

    Land cover

On the map, you can see that the site for the proposed wind farm is primarily open fields with some trees and hedgerows between the fields.

In the EIA, it was reported that the Swift Wind Farm would have four three-bladed, horizontal axis wind turbines, similar to the symbols on the map. The turbines would each be a maximum of 126.5 meters (415 feet) to tip height (that is, the tip of the rotor blade when it is upright.) The turbine locations were digitized from the map accompanying the EIA, as was the boundary of the proposed wind farm. The symbols are drawn at the size they would appear in the landscape, so if you zoom in and out, you will get a sense for how large these turbines would be.

Explore the Low Spinney Wind Farm

To see the size of wind turbines for another wind farm in the area, you will explore the Low Spinney Wind Farm, which has been in operation since November 2011.

  1. On the ribbon, click Bookmarks and choose Low Spinney Wind Farm.

    Bookmarks button

    The map zooms to a location with four large wind turbines.

    Low Spinney Wind Farm

    From the shadows in this image, you can tell that the turbines are quite tall. At 131 meters (429 feet), these turbines are nearly the same height to tip as those for the Swift Wind Farm. You can also see that the wind farm is located in a landscape of farms and pastures with a few isolated dwellings, much like the area around the proposed Swift Wind Farm.

  2. In the Contents pane, check the box next to the Low Spinney Wind Farm layer to turn it on.
  3. Click the green area around the turbines to see a street view of the wind farm in a pop-up, along with information about the source of the photograph and a link to the map that was used to digitize the turbine locations.

    Low Spinney Wind Farm pop-up

    In the photograph, you can see that the land is relatively flat and the turbines are quite tall and conspicuous.

  4. Close the pop-up and turn off the Low Spinney Wind Farm layer.

Explore other wind farms in the area

To see other wind farms that have been built or proposed in the surrounding area, you will explore the Wind Farms layer.

  1. Turn on the Wind Farms layer.
  2. In the Contents pane, click the layer name to see its legend.

    Wind Farms legend

    Some of the wind farms are built, others are under construction, and still others are being considered or have been rejected, perhaps leading to an appeal.

  3. To see the locations better, change the basemap to Topographic.
  4. In the Contents pane, point to the Wind Farms layer. Click the More Options button and choose Zoom to.

    Zoom to option

    The map zooms out to show you all the features in the layer.

    Wind farms

    The compilation of a wind farm map is challenging because the status of wind farm applications changes frequently. Even people who live in the area have a hard time keeping up with the proposals, rejections, appeals, and development of wind farms. So the status of the farms on this map may have changed from the time it was created.

  5. Investigate the geographic settings of the various wind farms by zooming to them and changing the basemap to Imagery with Labels.

    Note that the turbine locations for some of these wind farms are not evident in the imagery. This makes sense for those that were not approved or have not yet been built. However, you will also notice that for some that are active, the turbines may still not be shown in the imagery. This may be because the imagery is not current.

    You will see that most of the other wind farms are also located in open countryside with no large settlements nearby. This exploration helps you understand what kinds of sites have been selected for other wind farms in the area. It also gives you a sense of how much wind farm development there has already been in the area. This may play a part in local opposition to the establishment a of new site.

  6. Once you are done exploring the local wind farms, turn off the Wind Farms layer.

Explore local landmarks

Now you will explore two local landmarks that were cited in the EIA for the proposed wind farm. One of the concerns about building the wind farm was that the turbines would be visible from these nearby cultural assets—including the Churchover Conservation Area and Newnham Paddox Park and Garden.

  1. Zoom to the Churchover bookmark.

    Churchover Conservation Area

    Churchover is the village closest to the proposed wind farm. The Churchover Conservation Area, an "area of special architectural or historic interest, the character of which it is desirable to preserve or enhance,"[3] comprises the entire village as well as a portion of the nearby rural area. This is an area of concern because local authorities have a duty "to preserve those elements, including views, which together make up a familiar and attractive local scene."[3]

    Note the location of the proposed wind farm to the northeast of the village.

    The oldest building in Churchover is Holy Trinity Church, dating from the fifteenth century.

  2. Turn on the Holy Trinity Church layer and zoom in so you can see the size of the church and its spire.

    Holy Trinity Church

    The grounds to the north and east of the church are not landscaped and offer clear views into the countryside.

  3. Click the symbol to see a street view of the church.

    Street view of Holy Trinity Church

    Note that the church is on a slight rise and that the wall around the grounds (visible in the lower left of the picture) is quite low. The fifteenth-century spire is just over 20 meters (65 feet) high. The following graphic compares the turbines to the church.

    Dimensions turbines

    You can see that the turbine is more than 100 meters (328 feet) higher than the top of the church spire, and each blade of the turbine is about two times the length of the church (almost 10 average sedan car lengths). Note that the base of the turbine in this graphic is about 3 car lengths itself.

  4. Close the pop-up and turn off the Holy Trinity Church layer.

    Next, you will explore Newnham Paddox Park and Garden.

  5. Zoom to the Newnham Paddox View bookmark.
  6. Turn on the Newnham Paddox Park and Garden layer to see the location of the primary building on the estate.

    Newnham Paddox

    The view from the estate to the wind farm to the southeast is primarily open with few hedgerows and groves of trees to block the view.

  7. Zoom to the Newnham Paddox bookmark.
  8. Click the symbol to view its pop-up.

    Newnham Paddox pop-up

    This is the home of the Earl and Countess of Denbigh and a Registered Park and Garden of Special Historical Interest.

  9. Close the pop-up.
  10. If necessary, zoom out a couple of times to see more of the grounds.

    Newnham Paddox views

    Note that views from the buildings would likely be obscured by trees, but views from the grounds to the southeast, where the wind farm would be, are fairly open. This site is of concern because visitors to the estate may not appreciate it if the turbines are too visually conspicuous from the estate grounds.

Save the map

Before proceeding with the analysis, you'll save your map.

  1. On the ribbon, click the Save button and choose Save As.
  2. In the Save Map window, change the title to Swift Wind Farm Viewshed Analysis.
  3. Click Save Map.

Now that you are more familiar with the wind farm site and the surrounding area, you'll be better able to understand performing the viewshed analysis.


Perform a viewshed analysis

Using GIS, viewsheds can be calculated to show areas where observed objects, such as towers and turbines, can be seen, or, conversely, to show areas that can be seen from specified objects, such as steeples or observation decks. When performing this type of analysis for wind farms, you need to decide whether to compute the viewshed for the object from the tip of the rotor blade when it is in the most upright position, the rotor (which the blades are attached to), or some other part of the turbine. Your decision will have an impact on the viewshed analysis results.

Tall objects, such as wind turbines, solar power towers, and communication towers, will be visible for long distances in flat, open areas. In other areas, the terrain, as well as the presence of features—such as buildings, trees, and hedgerows—can make a significant difference to the actual view. The observer's visual acuity, curvature of the earth, and atmospheric refraction, which increases the visible distance to the horizon, also affect the visibility of an object. Although the earth's surface curves out of sight at a distance of about 5 kilometers (or 3 miles), the tops of tall objects may be visible above the horizon. At the same time, dust, water vapor, and pollution in the air will rarely allow you to see more than 20 kilometers (12 miles), even on a clear day. It is important to take these factors into account when assessing visual impacts through viewshed analysis.

The Create Viewshed tool takes into account atmospheric refraction and curvature of the earth, but not other factors, such as obstructing trees or buildings; therefore, viewshed analysis is often accompanied by on-the-ground investigations. For example, in the Swift Wind Farm EIA, 19 locations[1] were assessed to determine if their viewpoints would offer direct and uninterrupted views of the turbines. One requirement for viewshed analysis is data about the form of the landscape. In a GIS, the ground, or terrain, is commonly represented with a digital elevation model (DEM). Esri has compiled a number of elevation datasets in a format that is easy to use in your analysis and mapping. These datasets are used in the Create Viewshed tool. To learn more about the DEM data, see the Terrain layer description.

Perform the viewshed analysis

You'll perform a viewshed analysis from the tip of the rotor blade, and you'll compare that to a viewshed created from the base of the turbine. This will allow you to see how much the height of the object can impact the analysis.

  1. If necessary, open your Swift Wind Farm Viewshed Analysis map.
  2. Change the basemap back to Topographic.

    The Wind Turbines layer is a special layer created so you can see the proposed size of the turbines when you zoom in and out. It was created as a tile layer. The Create Viewshed tool requires point features, so you'll use the Turbines layer to perform the analysis in this lesson. It represents the same turbine locations without symbols designed to represent the actual height.

  3. Turn off all layers at once by pressing the Ctrl key while unchecking the box of any layer that is already turned on.
  4. Turn on the Turbines and Swift Wind Farm layers.
  5. Turn on the Study Area layer and zoom to it.

    Study area

    This layer shows the 25-kilometer distance from the turbines that you will use in the viewshed analysis. This 25-kilometer distance was used in the EIA to encompass an area "considered appropriate to cover all potentially material landscape and visual impacts resulting from the proposed Development."[2]

  6. In the Contents pane, point to the Turbines layer and click the Perform Analysis button.

    Perform Analysis button

    Tip:

    You can also access the Perform Analysis pane from the ribbon.

  7. In the Perform Analysis pane, click Find Locations and click Create Viewshed.

    Create Viewshed dialog box

    Notice that the tool displays a default height and default units.

    Tip:
    The default units for tools may be initially set by your organization's administrator but can be edited in your profile. In addition, you may have the option to change units for specific tool settings on the user interface. Analysis results, as reflected in tables and pop-ups, will always be reported in the units set in your profile, even if you choose different units in a tool setting.

  8. Verify that Point features that represent observer locations is set to Turbines.
  9. In the Create Viewshed pane, set Height of observer locations to 126.5 meters (or 415 feet).

    This is the height of the objects that will be observed, which, in this analysis, are the wind turbines.

  10. Set Height of other objects on the ground to 1.8 meters (or 6 feet).

    This is the height of the observer, so you will assume the average height of the people who will be viewing the turbines is 1.8 meters.

  11. Set Maximum viewing distance to 25 kilometers (or 15 miles).

    For the Create Viewshed tool, the optional Maximum viewing distance parameter is related to the resolution of the data used in the analysis and determines the extent of the viewshed. When the maximum viewing distance is less than or equal to 5 kilometers, and for areas where it is available, 10-meter resolution data will be used. If the maximum distance is greater than 5 kilometers but less than or equal to 15 kilometers, and where it is available, 30-meter resolution data will be used. Otherwise, if the distance is greater than 15 kilometers, 90-meter resolution data will be used. The maximum allowable viewing distance is 50 kilometers.

    Using a distance of 25 kilometers means that the coarsest-resolution data (90 meter) will be used in your analysis.

  12. Change the result layer name to Viewshed and add your name or initials to make it unique in the organization.
    Note:

    This will prevent your analysis results from conflicting with somebody else's in your organization.

    Create Viewshed tool

  13. Check the Use current map extent box.

    Use current map extent option

    Note:
    For the Create Viewshed tool, if Use current map extent is checked, only the features (turbines) that are visible in the current map extent will be analyzed. If unchecked, all features in the analysis layer will be analyzed, even if you cannot see them in the current map.

  14. Click Run Analysis.

    When the operation finishes, the Viewshed layer is added to the map and the Contents pane.

    Viewshed layer

    The viewshed you created identifies the areas that can be seen from the tops of the turbines and, conversely, areas from which the tops of the turbines can be seen.

    To see how the viewshed analysis varies depending on the assumptions you make, you'll compare your results with those of a second viewshed generated for the base of the turbine towers.

  15. In the Contents pane, point to the Viewshed yourname layer and click the Rerun Analysis button.

    Rerun Analysis button

    The Create Viewshed tool opens with the settings from the first time you ran the tool. You'll change the settings to create a second viewshed.

  16. Rerun the analysis with the following settings (substitute equivalent values if you are using U.S. standard units):
    • Set Height of observer locations to zero.
    • Set Height of other objects on the ground to 1.8 meters (5.9 feet).
    • Set Maximum viewing distance to 25 kilometers (16 miles).
    • Name the result layer Viewshed from Base, adding your name or initials to make it unique.

    Create viewshed from base

  17. Save the map.

Next, you'll explore the results of your analysis.


Explore the results

Previously, you created two viewsheds. In this lesson, you'll compare them.

To more easily see the differences, you'll change the symbols on the Viewshed from Base layer. Then, you'll explore the 25-kilometer Viewshed layer to better understand the output that this tool creates. Finally, you'll explore the visual impact from the two landmarks you investigated earlier.

Change the symbols

First, you'll symbolize the viewshed layer.

  1. If necessary, open your Swift Wind Farm Viewshed Analysis map.
  2. In the Contents pane, point to the Viewshed from Base layer and click the Change Style button.

    Change layer style

  3. On the Location (Single symbol) drawing style, click Options.

    Drawing style options

  4. Click Symbols to change the symbol.

    Symbols

  5. Click the blue color shown below (#0070FF) to change the fill color of the symbol.

    Fill option

  6. Click Outline and click the blue color shown below (#004DA8) to change the outline color of the symbol.

    Outline option

  7. Click OK.
  8. In the Change Style pane, click OK and click Done to finish changing the symbol.

    Two viewsheds

    Clearly there can be a radical difference in the size of the viewshed for wind turbines depending on whether it is generated for the upright tip of the blades or the base. This is important to note when performing or reviewing the results of viewshed analyses. An easy way to make the viewshed smaller is to use a lower value for the height of the objects being seen, so beware of analyses that alter the height to reduce the impact on visual aesthetics.

  9. Turn off the Viewshed from Base layer.

    Next, you will look at the attribute table for the Viewshed layer to see what fields are included in the results layer.

  10. In the Contents pane, point to the Viewshed layer and click the Show Table button.

    Show Viewshed Table

    The attribute table opens below the map view.

    Table

    Note that there are four area features distinguished by Frequency and Area Square Kilometers (or Area Square Miles, if your profile is set to U.S. standard units). The Frequency field records the number of turbines that can be seen from each area, though not which turbines. Because there are four turbines, the Frequency field has values between one and four; in areas with a value of one, you can see only one turbine, and in areas with a value of four, you can see all four turbines. For this viewshed, all four turbines can be seen from most of the viewshed area (761.35 square kilometers).

    The result layer also contains a DEM Resolution field, which records the resolution of the data used to create the viewsheds, which in this case is 90 meters. You can also see some information about the DEM data, including the name of the dataset and the agencies responsible for maintaining it.

  11. Click the X at the upper right to close the table.

    Next, you will change the symbology of the Viewshed layer to visualize how many turbines can be seen from within the viewshed.

  12. In the Contents pane, point to the Viewshed layer and click the Change Style button.
  13. For the attribute to show, choose Frequency.

    Frequency attribute

  14. At the bottom of the list of drawing styles, on the Types (Unique symbols) style, click Select.

    Types (Uniques symbols)

    Once the style is selected, a check mark appears to the right of its name, and the button text changes from Select to Options.

    Options button

  15. Click Options.
  16. Click the Symbols button to the right of Count to change the colors used to display the Frequency values.

    Change all symbols options

  17. Click the color ramp shown below (last one in the top row) to change the fill color of the symbols.

    Color ramp option

  18. Click Outline. Uncheck the Adjust outline automatically box, and then change Transparency to 100% so that it is not visible.

    Transparency setting

    Tip:

    Alternatively, you could set Line Width to 0 pixels.

  19. Click OK.
  20. In the Change Style pane, click OK and click Done to finish changing the symbol.
  21. Click the Viewshed layer name to see the symbols.

    Viewshed polygon symbol

    If only a single turbine can be seen, the area on the map will be shaded yellow; if two can be seen, the area will be orange. Areas in yellow-green will be where three turbines can be seen, and all four turbines will be visible in the green areas.

  22. Zoom to the Viewshed Symbols bookmark to see an area that has the four types of areas.

    Viewshed polygons

  23. Click a green area to see its pop-up.

    Viewshed pop-up

    For this area, all four turbines can be seen, and the area measurement is that of the entire green area.

  24. Close the pop-up.
  25. Click the other areas to see their pop-ups.
  26. Save the map.

Next, you will explore the viewshed for the two local landmarks that you looked at earlier.

Explore the viewsheds for the landmarks

You saw earlier that views from Churchover and Newnham Paddox would likely be affected by the erection of turbines on the proposed wind farm. You'll explore the viewshed analysis results to see if the turbines would be visible from these landmarks.

  1. Zoom to the Churchover bookmark to see how things would look from Churchover.

    Holy Trinity Church viewshed

    According to your analysis, the Swift Wind Farm turbines would be visible from every location in and near the village. This contrasts with the visual impact analysis in the EIA, which states, “There are few locations within the village (other than on its northernmost fringe) where direct and uninterrupted views of the proposed turbines would be available; indeed, for almost all areas within the village core there would be no or very restricted views of the turbines."[1]

    Recall that the viewshed analysis assumes unobstructed views—perhaps the EIA took obstructions into account. Nonetheless, your analysis suggests that the turbines would be visible from some locations within Churchover and the surrounding rural area that makes up the Churchover Conservation Area. Further analysis is needed to explore these discrepancies. The next step would be to perform on-ground investigations to verify the view from a variety of locations.

  2. Turn on the Newnham Paddox Park and Garden layer.
  3. Turn off the Turbines layer and turn on the Wind Turbines layer.
  4. Zoom to the Newnham Paddox View bookmark to see how things would look from the estate.

    Newnham Paddox viewshed

    Your analysis again indicates that the wind turbines would impact the visual aesthetics from this cultural site.

    The EIA states that views from within the estate “would be extremely limited and not considered to be significant. This is largely a result of substantial mature tree planting around Newnham Paddox and the additional screening effect of rising landform to the immediate east." [1] To check this, you will visually analyze whether trees and landforms would obstruct the view from Newnham Paddox.

  5. Turn off the Viewshed layer.

    Topo map of Newnham Paddox viewshed

    The Esri Topographic basemap shows terrain features, such as rises, through light shading and lines of equal elevation called contours. You will see little shading and very few contours (they will appear as light-gray unlabeled lines) between Newnham Paddox and the turbines, which indicates relatively flat land. This should lead you to question the EIA statement about the “rising landform,” so on-site analysis would be helpful to verify obstructions of the view by the terrain from this location.

  6. Change the basemap to Imagery to explore the land cover and other landscape features.

    Newnham Paddox view

    Note:

    Since you are not concerned with the names of features, you can use the Imagery basemap rather than the Imagery with Labels basemap you used earlier.

    The image shows few trees between Newnham Paddox and the turbines. This should lead you to question the statement in the EIA about "mature tree planting." Further investigation is clearly warranted.

  7. Save the map.

Now that you have explored the results of the analysis, you'll share the results with others.


Share your map with others

Before sharing your map, you'll often want to make a few edits to clean it up, including changing the basemap, setting the map extent, turning layers on or off, renaming layers, and removing layers.

Share your map

  1. If necessary, open your Swift Wind Farm Viewshed Analysis map.
  2. Change the basemap to Topographic.
  3. Zoom to the Study Area layer.
  4. Turn off the Newnham Paddox Park and Garden layer.
  5. Turn on the Viewshed layer.

    Viewshed map

  6. In the Contents pane, point to the Viewshed yourname layer. Click the More Options button and choose Rename.

    Rename layer

    Tip:

    Renaming the layer will make it more easily understandable for others who view your map.

  7. Change the layer name to Viewshed and click OK.

    Rename layer

  8. In the Contents pane, point to the Viewshed from Base layer. Click the More Options button and choose Remove.
  9. Also remove the Low Spinney Wind Farm layer.
  10. Save the map.
  11. On the ribbon, click Share.
  12. Choose to share your map with everyone or with your organization.

    Sharing options

  13. In the Update Sharing window, click Update Sharing.

    Sharing properties for layer

    Tip:

    The layers in your map must have the same sharing properties as your map. Any analysis layers you create are not shared by default, so you are now prompted to share them.

  14. To share your map with someone by email, copy the link to your map and paste it in your message to them.

    Link for map

  15. To share your map on Facebook or Twitter, click the related icon, if available.

    Social media

  16. Click Done.

You have now completed the viewshed analysis for the Swift Wind Farm. Imagine using this tool to perform similar studies, such as determining what you can see from the top of the Holy Trinity Church spire or from where you can see the Low Spinney Wind Farm. You can also use this tool to perform viewshed analyses for other locations in the world, because the DEM data is nearly global in extent.

You can find more lessons in the Learn ArcGIS Lesson Gallery.