Solve a spatial problem
Open and save the map
Start by opening the nassella tussock map in Map Viewer.
- In a web browser, go to the Analysis quick lesson - Nassella tussock ranges map.
Click Open in Map Viewer and sign in to your ArcGIS Online account if necessary.
Map Viewer opens to the Marlborough region of New Zealand. Commercial campgrounds are displayed, along with the known distribution of nassella tussock. The Nassella Tussock Range layer does not represent the density of the plant at a given location. A marked area may be heavily infested or it may have only scattered plants.
- On the ribbon above the map, click Save and choose Save As. Rename the map Analysis quick lesson - Your Name. Using your name in the title will ensure that the map title is unique in your organization. Click Save Map.
Explore the Perform Analysis pane
To carry out the analysis, you'll run tools from the Perform Analysis pane. First, you'll see how these tools are organized in ArcGIS Online.
- On the ribbon above the map, click Analysis.
The Perform Analysis pane appears. The tools are grouped into categories based on the type of analysis they perform. The Use Proximity tools help you answer one of the most common questions posed in spatial analysis: What is near what?
- In the Use Proximity group, click Create Buffers.
The Create Buffers tool opens in the Perform Analysis pane. Like all tools, it has options or parameters that need to be set.
the Information button beside Create Buffers.
Buffer the commercial campgrounds
Now you'll set the parameters for the Create Buffers tool and run it. The tool will create a new area layer containing 14 buffer features—one for each campground. The buffer features will be circles of a 1.5-kilometer radius centered on the campgrounds. Your assumption is that campers are most likely to come in contact with nassella tussock on walks, bike rides, and similar excursions. The 1.5-kilometer value seems reasonable, but it may also make sense to consider longer distances.
- In the Create Buffers tool pane, click the Choose layer containing features to buffer drop-down menu and click Commercial Campgrounds. In the Enter the buffer size text box, type 1.5. Click the adjacent drop-down menu of distance units and select Kilometers.
- Expand the Options dialog box and open the pop-up help for the Options parameter. You can choose between two Buffer Type settings: Overlap and Dissolve. Keep the Buffer Type set to Overlap.
Using the Overlap setting means that any buffers that are on top of each other will remain separate, whereas using Dissolve means that any areas that overlap will be combined into a single buffer.
- Change the Result layer name to Campground_Buffers and add your initials.
Adding your initials to the result helps ensure that it has a unique name. Each item in your organization must initially have a unique name to be saved.
- At the bottom of the Create Buffers tool pane, uncheck the Use current map extent box.
You are buffering all of the campgrounds, so you don't need to limit the extent of your analysis.
- Before running the tool, click Show credits to learn how many credits will be used to create your buffers.
- Click Run Analysis.
Now you'll hide the original layer in the map so that you can better see the buffer layer you just generated. Then you can zoom to the new buffer layer to examine it more closely.
- In the Contents pane, turn off the Commercial Campgrounds layer. Click More Options in the Campground_Buffers layer and click Zoom To.
To see nassella tussock inside the buffers, you need to change the style of the Campground_Buffers layer.
- In the Contents pane under Campground_Buffers, click Change Style.
Under Select a drawing style, choose Options.
- Click Symbols to change the symbol style.
- Change the fill to No color. Switch to Outline. Set Outline to black and Line Width to 1 px. Click OK to apply the changes.
- Click OK, and click Done in the Change Style pane to keep the changes.
The Campground_Buffers layer contains all of the original Commercial Campgrounds fields as well as a new field with the buffer size. You can see all of the fields in a dataset by viewing the layer's table.
- In the Contents pane under the Campground_Buffers layer, click Show Table.
The name and address attributes of the features have been copied from the corresponding commercial campgrounds. The Buffer distance in Kilometers field shows the buffer distance.
- Close the table.
- Zoom in and examine some buffers at close range to see whether they contain nassella tussock.
The majority of the nassella tussock range is outside of the campground buffers. However, some campgrounds do have nassella tussock within their 1.5 kilometer buffer.
- When you're finished, click Bookmarks > Campgrounds to return to an extent showing all of the campgrounds.
The Campground bookmark was created on the original map and was saved in your copy of the map. Bookmarks are a great way to save time if you are often zooming back and forth to different map extents.
- Save your map.
Select buffers containing nassella tussock
The next part of the analysis is to identify the buffers that contain nassella tussock. For this, you need a tool that finds features in one layer (Campground_Buffers) according to whether they have areas in common with features in another layer (Nassella Tussock Range).
- Click Analysis to open the Perform Analysis pane.
Expand the Find Locations group and click the Find Existing Locations tool.
The Find Existing Locations tool selects existing features in your study area that meet a series of attribute or spatial criteria you specify.
- Click the Choose layer containing features you want to find using attribute and spatial queries drop-down menu and select Campground_Buffers.
- For Build a query to find features, click Add Expression to open the Add Expression dialog box.
The Find Existing Locations tool uses both attribute and spatial expressions to find features that meet a specific set of criteria. The most common spatial relationship used in Find Existing Locations is intersects, which can be used to find features that overlap or touch.
- In the Add Expression dialog box, change the relationship to intersects and the second layer to Nassella Tussock Range. Click Add.
The features in the input feature layer will be selected. This is the correct setting because you want to know which campgrounds are affected, not which patches of nassella tussock are affected.
- Change the Result layer name to Campgrounds_Within_Range Your Initials. Again, you can uncheck Use current map extent and click Show credits. Click Run Analysis to run the tool.
Four buffers intersect with the nassella tussock range.
It may not surprise you that two of the selected buffers lie in areas where nassella tussock is prevalent. But what about the other two? Do the four selected buffers have a geographic relationship that sets them apart from the others? You'll look at some of the other layers in the map to see if they help you answer this question.
- In the Contents pane, turn on the Roads layer.
The four selected buffers are linked by principal highways. This suggests that the road network facilitates the spread of nassella tussock. On the other hand, many unselected buffers are also linked by highways. It would be interesting to know which campgrounds are visited most often and whether vacationers typically visit multiple campgrounds, but these questions are beyond the scope of this lesson.
- Turn off the Roads layer and turn on the Populated Places layer.
Three of the four selected buffers intersect populated places. At the same time, many populated places have no nassella tussock near them. While this brief investigation was inconclusive, spatial selections are a good way to discover meaningful patterns in your data and stimulate ideas for further analysis.
- Turn off the Populated Places layer.
- Save your map.
Quantify nassella tussock within buffers
In the third part of the analysis, you want to find out how much nassella tussock lies within the selected buffers. Why does that matter? For public education, it may be useful to provide campgrounds with a bulletin on whether nassella tussock has been found in the area, and, if it has been found, whether or not it is widespread. For researchers, a quantitative measurement is a baseline for comparison in coming years.
The tool you will use is Summarize Within.
- Click Analysis to open the Perform Analysis pane.
Under Summarize Data, click Summarize Within to open the tool.
One of the functions of Summarize Within is to calculate how much area from one layer falls within another layer—this is what you want to do for your analysis.
- For Choose an area layer to summarize other features within its boundaries, choose Polygon and Campgrounds_Within_Range.
- For Choose a layer to summarize, select Nassella Tussock Range. In the Add statistics from the layer to summarize parameter, change the Sum Area in measurement to Hectares.
A hectare is a metric unit of area equal to 10,000 square meters or roughly two and a half acres.
- Change Result layer name to Tussock_Within_Buffers Your Initials. You can uncheck Use current map extent and click Show credits.
Click Run Analysis to run the tool.
When the tool completes successfully, the Tussock_Within_Buffers layer is added to your map.
- The Tussock_Within_Buffers layer contains features that overlap exactly with the Campgrounds_Within_Range layer, but the Tussock_Within_Buffers layer contains the summary statistics. In the Contents pane, turn off the Campgrounds_Within_Range layer to make it easier to work with Tussock_Within_Buffers.
The Tussock_Within_Buffers layer has four features, corresponding to the four selected campground buffers. You'll change the style of the layer so you can see through it.
- In the Contents pane under Tussock_Within_Buffers, choose Change Style. Switch the Choose an attribute to show parameter to Show location only. Under Select a drawing style, click Options.
- Click Symbols to change the symbol style. Choose a fill on the gray scale. Switch to Outline and choose black. Click OK to apply the changes. Change the overall Transparency to 25 percent and click OK. Click Done to keep the changes you've made.
- In the Contents pane under Tussock_Within_Buffers, click Show Table.
The Summarized area in Hectares field shows the total area of nassella tussock within each campground range. The largest area of nassella tussock is at the Awatere Settlers Motor Camp, where there are more than 83 hectares. The smallest area of nassella tussock overlaps the Blenheim TOP 10 Holiday Park and has approximately 0.25 hectares. Keep in mind that the Nassella Tussock Range layer represents areas in which the plant has been found, not the actual plant density.
- Save your map.
In 25 minutes, you found publicly available data, determined which campgrounds have an overlapping range with nassella tussock, and calculated the total area of nassella tussock within each campground range. What's next?
Perform a similar analysis to solve the nassella tussock problem using the powerful geoprocessing tools in ArcGIS Pro.
Explore ArcGIS Online on your own and discover what else is possible. A few ideas are as follows: