Using the Analyze Area Tool for Ecological Monitoring
This article will cover:
- Using Analyze Area
- Year Over Year comparisons
- Category breakdown charts
- Saving Analyze Area charts in notes
- Exporting Analyze Area values
Analyze Area allows you to easily visualize seasonal patterns and year-over-year changes in ecological conditions. Drill down to specific areas of interest within a property and see how conditions have changed over the last several months or years. This feature can be used in a variety of applications, such as determining the timing of a timber harvest by reviewing seasonal cycles in vegetation vigor, or visualizing fluctuations in water and surface moisture presence in wetland areas.
We derive these data from Sentinel-2 data, an ensemble of two satellites – the first launched in late 2015 and the second in 2017. The 10-meter resolution Sentinel-2 data are captured almost every week, making them ideal for tracking changes over time. You can explore details on vegetation, surface water, surface moisture, and snow for targeted areas of interest. Find more information on these indices in the Public Imagery and Data Layers article.
Using Analyze Area
Launching, choosing layer, selecting chart type
Once you’ve selected a property, select the Analyze Area button on the right side of the Map Property View. You can then draw a boundary around your targeted area of interest by clicking to drop each point and double-clicking to close the polygon, or choose to select the whole property within the dialog box.
Once you’ve drawn your polygon, the Analyze Area box will populate to show how conditions have changed over time. You can choose from vegetation, water, or snow and select the period you would like to visualize in the graph. You can also make a note to associate with this particular part of your property for easy reporting or future reference.
Choose from vegetation, surface water, surface moisture, and snow data layers using the drop-down menu on the left side of the modal. Change the time span of the graph using the dropdown on the right-hand side of the modal. Explore different graph types using the presets Average Value, Area in Range, and Area by Category. Average Value will graph the average pixel value in the drawn polygon for the selected index. Area in Range, shown in the example below, allows you to define a metric range of interest and graphs the percent of the selected area within that range. Area by Category graphs the percent of the selected area within a specific metric range that corresponds to a category (Ex: Water, Not water).
Exploring chart data
Once you have a graph loaded, you can use your mouse wheel or trackpad to zoom in and out on specific months and pan horizontally by clicking and dragging the chart body. To reset the visible time range, click on the refresh icon to the left of the x-axis.
Select a point on the Analyze Area chart to view the index layer image of the corresponding date. To enter Compare Mode, select one point on the chart then hold shift and select a second point. Hover over a point on the chart to display the corresponding date and the index value at that point in time.
Year Over Year comparisons
The Analyze Area year-over-year chart allows you to compare trends from multiple years on the same annualized axis. You can look at the entire calendar year or compare particular months of interest by zooming in on the graph. Use this chart to look at trends between years, find outliers, and identify areas for closer analysis. You’ll see each year of data represented by a separate line on the chart. If you prefer to hone in on specific years, you can toggle individual years on and off by clicking each year at the bottom of the chart
Category breakdown charts
For category layers, including NLCD landcover from USGS and the European Space Agency's WorldCover data, we now display a bar chart breakdown. This can be a great way to compare land cover change over multiple years.
The chart shows % of the selected polygon by default, and you can see the area associated with each category by hovering your mouse over each part of the chart. If the data layer you've selected has multiple time steps, you can select and de-select those in the date dropdown. Currently, this type of chart cannot be saved in notes.
Saving Analyze Area charts in notes
You can also save the chart from Analyze Area in a Note. From the Analyze Area tool, simply add a description of what you're seeing below the graph and click "Create" to save this graph as a note, and be sure to check the box for “Include Analyze Area graph”. This will ensure that the chart will be included in the reports you generate about this property. You can also zoom in on the graph from the Notes pane or in the Report as needed.
Note that you cannot add a note to an Analyze Area chart created for a multi-polygon. In this scenario, the notes section will be greyed. You will only run into this issue when you use the “select entire property” option to launch Analyze Area on a multi-polygon property.
If you made a polygon note, you can open Analyze Area directly from the note by clicking the three dots on the top right. This will allow you to dig into trends in the data for that note's geometry.
Exporting Analyze Area values
To export the values from an Analyze Area chart, click on the three dots icon in the upper-right corner, and select the “Export graph CSV” option. You can also select “Export shapefile” to download the polygon used for the Analyze Area analysis.
The CSV includes three columns: date, index value, and area. If the “Average Value” option is selected, the acres column will refer to the total analysis polygon area (e.g., the entire property boundary). If the “Area in Range'' or “Area by Category” options are selected, the acres column will refer to the acreage that falls within that range at each given date.