The Create Space Time Cube By Aggregating Points tool summarizes point datasets into a netCDF data structure by aggregating the points into space-time bins that form a cube. Each bin within the cube contains a count of the number of points that occurred at the bin location for the time-step interval specified. Additionally, the cube may contain one or more Summary Fields with statistics for those fields in each bin.
The Emerging Hot Spot Analysis tool takes the netCDF cube as input, runs a space-time hot spot analysis, and identifies trends in the aggregated count data or summary fields, such as new, intensifying, diminishing, and sporadic hot and cold spots. The Local Outlier Analysis tool also takes the netCDF cube as input and runs an interpretation of the Local Moran's I statistic to identify statistically significant clusters and outliers in the context of both space and time. The netCDF cube is updated with the results of these analyses in the form of several new variables. The Create Space Time Cube By Aggregating Points, Emerging Hot Spot Analysis, and Local Outlier Analysis tools are available in both ArcGIS Desktop and ArcGIS Pro.
The data stored in the space-time netCDF cube can be visualized in either two or three dimensions using the visualization tools in the Utilities toolset. To visualize the space-time cube in 3D, you must use either ArcGlobe or ArcGIS Pro. For optimal 3D visualization, ArcGIS Pro is recommended. Visualization of the cube is useful for several reasons.
- It can help you understand the structure of the space-time cube and how the process of aggregation into the cube works.
- It can also offer insights into the results of Emerging Hot Spot Analysis and Local Outlier Analysis, providing evidence that can help you understand the result categories themselves.
- Additionally, visualizing Summary Fields can help you understand how confident you can be in subsequent analyses by displaying the spatial pattern of empty bins that had to be estimated.
Visualizing the Space Time Cube in 3D
- Open ArcGIS Pro.
- Open a scene. To open a scene so the results of the tool can be rendered in 3D, go to the Insert tab, click New Map, and choose New Scene.
- Set the elevation surface to zero. Because time is used as the vertical axis in visualizing the space-time cube, it is important for accurate interpretation that all locations on the ground are at the same elevation. This way, all time-step intervals start at the same base. In order to do this, the default elevation services need to be shut off. To turn off elevation services, right-click the new Scene in the Contents pane and click Properties. Browse to the Elevation Surface tab, expand Ground, and remove the elevation services that are being used by default.
- Access the Utilities toolset, which is located in the Space Time Pattern Mining toolbox, and open the Visualize Space Time Cube in 3D tool.
- First choose a Cube Variable to explore. After Create Space Time Cube By Aggregating Points has been run, variables stored in the cube will include Count as well as any Summary Fields that you chose to aggregate when creating the cube.
- Next choose a Display Theme for the Cube Variable chosen. The Value option will allow you to see the raw numbers associated with aggregation. You will also have the option of visualizing Hot and cold spot results if you have run Emerging Hot Spot Analysis and Cluster and outlier results if you have run Local Outlier Analysis on that particular variable. Summary variables will also have the option of visualizing the Estimated bins so you can see exactly which bins were filled in based on your decisions in Create Space Time Cube By Aggregating Points.
- Finally, choose where to save the Output Space Time Cube Features and Run the tool.
See Navigation in ArcGIS Pro to learn more about navigating and exploring your 3D scene.
Explore 3D Results Using the Time Slider
The 3D space-time cube can be further explored using the time slider. The steps to utilize the time slider are as follows:
- From the Contents pane, double click the output of the Visualize Space Time Cube in 3D and choose Time.
- Set Layer Time to Each feature has start and end time fields. The Start Time Field and End Time Field will automatically populate and the Time Extent will be automatically calculated. Click OK.
- Navigate to the Time tab and enter a Span of 0. Uncheck the Use Time Span option and set the Step Interval to the Time Step Interval of the Input Space Time Cube.
- Enable time by clicking the clock icon to the left of the time slider and use the arrows or play button to explore the results in your space-time cube.
Visualizing the Space Time Cube in 2D
- Open ArcGIS Pro.
- Access the Utilities toolset, which is located in the Space Time Pattern Mining toolbox, and open the Visualize Space Time Cube in 2D tool.
- First choose a Cube Variable to explore. After Create Space Time Cube By Aggregating Points has been run, variables stored in the cube will include Count, as well as any Summary Fields that you chose to aggregate when creating the cube.
- Next choose a Display Theme to display the chosen Cube Variable. Locations with data will allow you to see all of the locations that contain data for the chosen variable, and the Trends option will show you where values have been increasing or decreasing over time (the results of the Mann-Kendall statistic run on the chosen Cube Variable for each location). Both Locations with data and Trends are always available. Hot and cold spot trends will show you where hot and cold spot z-scores are increasing or decreasing over time (the results of the Mann-Kendall statistic run on the z-scores of the space time hot spot analysis for the chosen Cube Variable), and Emerging Hot Spot Analysis results re-creates the results you saw when you ran the Emerging Hot Spot Analysis tool. Both Hot and cold spot trends and Emerging Hot Spot Analysis results are only available when Emerging Hot Spot Analysis has been run on the chosen Cube Variable. Local Outlier Results re-creates the results you saw when you ran the Local Outlier Analysis tool for the chosen Cube Variable. Number of estimated bins will show how many bins were estimated at each unique location, allowing you to see if there is a spatial pattern of places with missing values. If entire sections of the map have high numbers of estimated bins, that area might be best left out of the analysis. Locations excluded from analysis shows those places that had data, but had empty bins that could not be filled because they did not meet the criteria for estimation. Both Number of estimated bins and Locations excluded from analysis are only available for Summary Fields.
- Choose where to save the Output Features and Run the tool.