In the previous lesson, you familiarized yourself with the study area. In this lesson, you'll perform analysis to calculate the impact that roads have on deforestation. First, you'll add a layer showing the extent of deforestation. Then, you'll quantify the percentage of land that is deforested within a certain distance from roads. By finding the relationship between existing roads and deforestation, you'll later be able to estimate the deforestation prevented by the proposed road's prohibition.
If you haven't completed the previous lesson(s), start this module by downloading the project package.
Although you looked at deforestation in the last lesson, now you'll begin a more thorough exploration to understand existing deforestation patterns in Rondônia. You'll start by adding a layer that shows deforestation in the state.
- If necessary, open your Rondonia Deforestation project in ArcGIS Pro.
- At the bottom of the Symbology pane, click the Catalog tab.
You can switch between open panes by using the tabs.
If you closed the Symbology pane, you can also reopen it by clicking any of the layer symbols listed in the Contents pane.
- In the Catalog pane, expand Databases, then expand the Rondonia geodatabase. Drag the Deforested_Area feature class into the Contents pane below Roads.
The Deforested Area layer is added to the map using a random color. This data was derived from satellite imagery using a classification technique to identify forested areas and cleared land.
- If necessary, zoom in until you see the Deforested Area layer.
Because patterns of deforestation closely follow roads, it may be difficult to see the layer under the unofficial roads layer.
- Click the symbol for Deforested Area. In the Symbology pane, click the Properties tab.
- Expand the Color menu, and at the bottom of the window, click Color Properties.
The Color Editor window appears. The Color Editor allows you to specify color by various color models, such as RGB, HLS, and HSV. You can also modify the transparency of a chosen color.
- In the HEX # box, enter the color code E1E1F2click OK, then click Apply at the bottom of the Symbology pane.
The deforested area layer is now symbolized in a light purple. The color contrasts with the layers currently on the map. The layer's default outline obscures some of the layer, though, so you'll remove it.
- Change the Outline color to No Color and click Apply.
The solid color of the layer covers up the deforestation visible on the basemap. To show both layers at the same time, you'll adjust the transparency.
- On the ribbon, click the Appearance contextual tab.
If the tab is not visible, in the Contents pane, click Deforested Area to select the layer.
- In the Effects group, change the transparency to 50 percent.
- In the Contents pane, right-click Deforested Area and choose Zoom To Layer.
The layer has only one feature. This is a multipart feature: a feature composed of many noncontiguous elements. Deforestation typically occurs in small parcels, not large unbroken swaths. At this map scale, it's difficult to see deforestation in much detail. You'll zoom in to look closer, but first you'll bookmark the current map extent. With a bookmark, you can quickly navigate to specific map extents.
- On the ribbon, on the Map tab, in the Navigate group, click Bookmarks.
- Click New Bookmark. In the Create Bookmark window, name the bookmark Rondonia and click OK.
Now that you have a bookmark, you can zoom around the map and return quickly to a view of the entire state.
- On the ribbon, in the Navigate group, make sure the Explore button is selected.
The Explore button will ensure that when you draw your area of interest, you zoom to the area instead of selecting it.
- Hold the Shift key and draw a rectangle around the northwest corner of Rondônia.
The map zooms to the extent of the rectangle. Once zoomed in, you can see the deforestation in more detail.
- In the Contents pane, uncheck the Roads layer to turn it off.
Deforestation is often patchy, following roads.
Typically, small strips of forest are deforested through a process called slash-and-burn agriculture. In slash-and-burn-agriculture, farmers cut and burn plots of forest to create fields. The burned biomass serves as fertilizer for agriculture on the cleared land. This agricultural technique has been practiced for centuries throughout the world, including the Amazon. In small amounts, slash-and-burn agriculture can be sustainable. But when widespread, massive areas are cleared in a small amount of time, and it can drastically affect an ecosystem.
Another noticeable pattern is that deforestation sometimes ends abruptly with fairly sharp boundaries, as in the following image:
In the above example, the boundaries are defined by protected areas, which either prohibit or greatly restrict deforestation. Protected areas come in two types: protected forests and indigenous territory. Feature classes for both categories are in the Project Data geodatabase. You can add both to explore, but for this project you only need the data on protected forests.
- On the ribbon, click the Map tab. Click Bookmarks and choose Rondonia.
- From the Catalog pane, add the Protected_Forests layer below Roads.
The Protected Forests layer is added to the map with a random symbology. Because it is a natural forest area, you'll symbolize it in green.
- In the Contents pane, click the symbol and change the color to HEX # 32936F.
- On the Appearance tab, change the transparency to 50 percent.
The protected areas seem to be an effective deterrent of deforestation. Now that you can see one of the preventive measures against deforestation, you'll investigate its causes. Earlier, you turned off the Roads layer because the dense road network obscured other layers on your map. Now, you'll take a closer look at those roads to see how they relate to deforestation.
- Zoom back to the northwest corner of Rondônia and turn the Roads layer on.
- On the ribbon, on the Appearance tab, in the Effects group, click Swipe and make sure the Roads layer is selected in the Contents pane.
When you hover over the map, the pointer changes to an arrow.
- Click on the map and swipe up and down to turn visibility for the Roads layer on and off.
There is a strong relationship between roads and deforestation. In fact, 95 percent of deforestation in the Amazon rain forest occurs within 5.5 kilometers of a road. Roads allow access to the otherwise impenetrable rain forest and facilitate the transportation of lumber. Unlike official roads, which connect cities, unofficial roads access deeper areas of the rain forest and connect rural properties.
Your goal is to estimate how much deforestation a proposed road would cause if its construction were allowed. To make this estimate, you'll first find how much deforestation is associated with existing roads.
Find deforestation near existing roads
Before you begin your analysis, you'll select a sample area of the existing road network. The road network is massive, with over 20,000 features. Performing analysis on the entire thing would take a lot of time. Selecting a sample area may affect your results slightly, but not much.
- In the Contents pane, turn off all layers except for Roads and the Imagery basemap.
To quickly turn all layers on or off, press the Ctrl key and click one of the layer check boxes.
- On the ribbon on the Map tab, in the Selection group, click Select and draw a rectangle around the northwest portion of the state.
Your selection doesn't have to match exactly.
The features in the box are selected on the map. Some roads that extend outside the selection area are selected. If part of a feature is in the selection area, the entire feature is selected.
Now that you have a sample of roads selected, you can start performing analysis on the sample. To do this, you'll use the Buffer tool. The buffer tool creates an offset at a specified distance from the input features. Using the deforestation data, you can calculate that most deforestation happens within 5.5 kilometers of roads, so you'll create a polygon feature representing that area.
- On the ribbon, click the Analysis tab. In the Geoprocessing group, click Tools.
The Geoprocessing pane appears. A customizable view of favorites is displayed. Like the Gallery in the Symbology pane, these are frequently used choices.
- In the Geoprocessing pane, under Favorites, click Buffer (Analysis Tools).
The Buffer tool parameters open in the Geoprocessing pane. In the tool pane, you'll set your input dataset and a few parameters needed to run the tool. One of those parameters sets the distance of your buffer, or how far away from the input features the buffer area will extend. You already know that 95 percent of deforestation in the Amazon occurs within 5.5 kilometers of roads. This is a good distance for your buffer, as relatively little deforestation occurs beyond this distance.
- For Input Features, choose Roads and for Output Feature Class, make sure that the name is Roads_Buffer.
When you run a geoprocessing tool on a layer with selected features, the tool will only process the selected features.
- For Distance, type 5.5, and change the Linear Unit to Kilometers.
The only other parameter you need to change is Dissolve Type. By default, the Buffer tool creates a buffer for each feature in the input layer. Because your Roads layer selection has many features and those features are very close together, the Buffer tool would create a large number of overlapping buffer features. By changing the Dissolve Type parameter, the Buffer tool will create a single feature as its output.
- For Dissolve Type, choose Dissolve all output features into a single feature.
If you are unsure of what a parameter does or what option to choose, hover over the parameter and click the information button that appears.
- Leave the rest of the defaults and click Run.
When the tool is finished running, the resulting layer is added to the Contents pane.
- In the Contents pane, drag the Roads_Buffer layer below Deforested Area.
A significant portion of the buffer overlaps with the Deforested Area layer, although not uniformly. The northwestern part of the buffer has many areas that are near roads but have relatively little deforestation.
To calculate the percentage of the buffer that is deforested, you'll need a layer of deforestation within the buffer. You can create this layer using a geoprocessing tool called Clip. The Clip tool clips the extent of one layer to the extent of another.
- On the ribbon, on the Map tab, in the Selection group, click Clear.
The selection of roads is removed.
- In the Geoprocessing pane, click the back button.
- Search for the Clip tool and select Clip (Analysis Tools).
- For Input Features, choose Deforested Area. For Clip Features, choose Roads_Buffer.
- For Output Feature Class, make sure Deforested_Area_Clip is saved to the default geodatabase and click Run.
Once the tool finishes, the layer is added to the map.
Calculate the percentage of deforested area near roads
You've created two layers. One shows the area within 5.5 kilometers of the roads in your sample area. The other shows deforestation within that buffer. Your next goal is to calculate the percentage of the buffer that is deforested. To find the percentage, you'll calculate a new attribute field.
- In the Contents pane, right-click the Deforested_Area_Clip layer and choose Attribute Table.
The attribute table opens. This table displays all the data, or attributes, associated with features. The Deforested_Area_Clip layer has two fields of geometry that are automatically created for all polygon feature classes: Shape_Length (perimeter) and Shape_Area.
- Click the Shape_Area value to select it, then press Ctrl+C to copy it.
The unit of measurement is not given in the table, but specified in the layer's coordinate system information. The projection of the data is South America Albers Equal Area. Output layers made from geoprocessing tools use the same projection as their input. Below the projection name is technical information about the projection, including its linear unit (the unit of measurement used by the projection). For the South America Albers projection, the linear unit is meters. Thus, the Shape_Area field in the attribute table is in square meters.
Your shape area may vary depending on the size of your selection and the buffer process.
- In the Contents pane, right-click the Roads_Buffer layer and open the attribute table.
- Next to Field, click Add.
The Fields table opens. This table allows you to edit the field name, alias, data type, and other specifics.
- At the bottom of the Fields table, click the highlighted new field and name it Percent_Deforested.
- For Alias, type Percent Deforested, and for Data Type, choose Double.
The field type determines what kind of values the field can have. The Double type allows numerals with decimals. The Alias gives the field a more conventionally readable name. Field names can only have text, numerals, and underscores. Aliases can contain other characters. The field alias is displayed in the table and Contents pane, while the actual name is stored in the data.
- On the ribbon on the Fields tab, in the Changes group, click Save.
- Close the Fields table.
- In the Roads_Buffer table, right-click Percent Deforested and choose Calculate Field.
The Calculate Field tool opens in the Geoprocessing pane. The Calculate Field tool is similar to the Select By Attributes tool in that it prompts you to build an expression. The tool gives you standard mathematical operators and functions as well as existing fields in the attribute table to help build your expression.
To find the percentage, you'll divide the area of the Deforested_Area_Clip layer by the area of the Roads_Buffer layer and multiply the result by 100. The equation for the data shown here is as follows:
- In the Percent_Deforested= box, paste the number you copied from the Deforested_Area_Clip.
- In the list of operations, click the division sign. In the Fields list, double-click Shape_Area.
- Click the multiplication button and type 100. Click Run.
The initial area value in your expression may be different depending on the sample area you chose.
When the calculation is complete, the percentage value will be added to the Roads_Buffer attribute table. Based on the example area values, the value returned was about 48 percent. Your value may differ, but probably not by more than a couple of percentage points.
You now know the percentage of land within 5.5 kilometers of roads that is deforested. If a new road were built in this sample area, you could predict that a similar percentage of land within 5.5 kilometers of that road would become deforested.
Now that you have this value, the Deforested_Area_Clip layer is no longer necessary. You'll remove it from your map. You'll keep the Roads_Buffer layer because it has the percentage value in its attributes, but you'll turn off the layer.
- Close the Attribute Tables for Roads_Buffer and Deforested_Area_Clip.
- In the Contents pane, turn off the Roads_Buffer layer. Right-click Deforested_Area_Clip and choose Remove.
The layer is removed from the map. It is still saved in the Rondonia geodatabase, and can be added to the map again if necessary.
- Return to the Rondonia bookmark and save the project.
In this lesson, you calculated the impact of deforestation in Rondônia due to the road network. In the next lesson, you'll use this percentage to predict the impact of the proposed road.