In Part I, we will explore tools to visually explore and compare multiple datasets, such as animations and layouts with multiple map frames. In Part II, we will explore tools to statistically compare multiple datasets, including calculating percent area and creating graphs. We will use both techniques to interpret our data and explore how vegetation within our study area changes over time as it responds to changes in water levels.
Note: You should not complete this step until you have read through all of the pages in Lesson 4. See the Lesson 4 Checklist for further information.
Part I, we will explore several tools and technique to make it easier to visually interpret patterns in your data using ArcGIS. These can be especially helpful when you have multiple datasets to compare.
Year | water Level (m) | High, Med, Low |
---|---|---|
1962 | 173.9 | |
1973 | 174.9 | |
2005 | 174.2 |
Based on the Lake Erie Hydrograph, how do the water levels for 1962, 1973, and 2005 compare to the long term averages for Lake Erie? Which years had the highest and lowest water levels between 1920 and the present?
One of the challenges of looking at time-series data of the same location is that all of the datasets overlap each other. It is very difficult to see all of the datasets at the same time if you have them all on the same map, especially if they are polygon files.
In this lesson, we arranged the layers within each group chronologically. You could also arrange them in a different order, such as by their water level (low, medium, high) to visualize how the vegetation changes correlate with water level changes.
Make sure you have the correct answer before moving on to the next step.
When you preview your animation, you should see one layer turned on at a time beginning with the VegGrp_60s and ending with the VegGrp_00s.
If your data is not close to the example, go back and redo the previous step. You’ll need to clear the animation first by going to the View tab, Animation group, select Remove.
If you want to be able to view your animation outside of ArcGIS, you can export your animation to a video file. You can also make your animations more sophisticated by exploring the available animation tools and options within ArcGIS. For example, you can add looping, string multiple animations together, add time-series labels, and add graphs that update over time along with your animation. You can find more information, such as help articles, sample animations, and tips in the Esri help topics.
Animations are great for emailing to a client or adding to a presentation. However, if you want to print your maps, you need to create a layout. We are going to create a layout with multiple map frames to make it easier to compare our data over time. When working with multiple map frames that show similar information, it is easier to set the symbology, extent, and scale in one map, then make copies of the map, instead of setting up each map separately.
The final map layout should include all of the following elements:
In ArcGIS Pro, if two or more map frames reference the same map, any manipulation to the layers in the map (such as turning any layer on or off or zooming in or out) affects both map frames because the layout is referencing the same Map. To bypass this, a separate Map must be referenced for each Map Frame in a Layout. Go to the Insert tab, Project group, and select New Map. Insert six New Maps to your project (each should default to a different name Map, Map1, Map2, Map3...).
Switch back to your original Map. Switch off the Open Street Map Basemap for now, as it will increase the loading time while you are setting up your layout. Adjust your scale and extent, right-click on “Study_Site” in the Contents pane > Zoom to Layer. Turn on the 60sVegGrp layer.
Hold down the control key and highlight the "Study_Site", "OttawaNWR", "Vegetation Group" and "OpenStreetMap" layers in the Contents pane. Right-click and select Copy.
Go to Map1, right-click on the map name in the Contents pane > Paste. Turn the Study_Site, OttawaNWR, and 70sVegGrp layers on. Do the same in Map2 but turn Study_Site, OttawaNWR, and 00sVegGrp layers on.
Switch back to your original Map. Adjust your scale and extent, right-click on “Study_Site” in the Contents pane > Zoom to Layer.
Hold down the control key and highlight the "Study_Site", "OttawaNWR", "Invasive Group" and "OpenStreetMap" layers in the Contents pane. Right-click and select Copy.
Go to Map3, right-click on the Map name in the Contents pane > Paste. Turn the Study_Site, OttawaNWR, and 60s_Invasive layers on. Do the same in Map4 but turn Study_Site, OttawaNWR, and 70s_Invasive the layers on. And, then in Map5 turn on Study_Site, OttawaNWR, and 00s_Invasive the layers on.
Go to Map6, right-click on the Map name in the Contents pane > Paste. Turn the Study_Site, and OttawaNWR layers on.
Adding neatlines to your map layouts helps to visually group elements together. This is helpful when your map has a lot of information. Go to the Insert tab, Graphics and Text group, and then click on Rectangle. After you place the rectangle in the layout, you can select it and right-click to format and adjust the symbology settings of the neatline.
Visually exploring your data is a good way to start interpreting your results. However, it is difficult to determine the magnitude of change just by looking at a map. Calculating statistics allows you to have actual numbers to work with, allowing you to say that “variable x increased by 12%” instead of “variable x increased.”
While calculating statistics, it is very easy to make mistakes such as typos, choosing incorrect input layers, or using incorrect order of operations. To avoid possible errors, you should first visually explore your data so you have an idea of the trends that exist in the data. After calculating statistics, you can compare your results to your visual interpretation to make sure your statistical results seem reasonable.
Study Year | Water Level (High, Med, Low) | Area Open Water (sq m) | Area Emergent Vegetation (sq m) | Area Invasive Species (sq m) | Area Controlled Invasive Species (sq m) |
---|---|---|---|---|---|
1962 | |||||
1973 | |||||
2005 |
Which year has the most emergent vegetation? Which year has the most open water? Did you find it difficult to compare such complex numbers (lots of digits and decimal places)?
Study Year | Water Level (High, Med, Low) | % Tot. Area Open Water | % Tot. Area Emergent Vegetation | % Total Area Invasive | % Tot. Area Controlled Invasive |
---|---|---|---|---|---|
1962 | |||||
1973 | |||||
2005 |
Which year has the most invasive species? Which year has the least open water? How does this correlate with water levels? Which files have the most missing data? After comparing several datasets using calculated areas and percent total areas, which technique do you find is easier to detect trends between multiple datasets?
After experimenting with both visual and statistical techniques to determine trends in your data, can you think of any scenarios in which one is preferable over the other?
That’s it for the required portion of the Lesson 4 Step-by-Step Activity. Please consult the Lesson Checklist for instructions on what to do next.