Searching for and understanding GIS data

To explore accessing and using geospatial data, we will start with an example data scenario. The map below shows census tracts graded by social vulnerability index, layered against the locations of known toxics release facilities in Massachusetts.

Map layers displayed in desktop GIS program, QGIS. On first glance, this looks like it may reveal a pattern, but we need to understand the dots.

• The Social Vulnerability Index (SVI) is a dataset that garners census variables to identify and rank communities based on their vulnerability to environmental hazards or other emergencies.
• Comparing the locations of vulnerable populations against environmental hazards such as toxics release facilities can help identify disproportionately burdened communities and prioritize health interventions.

Where to obtain the data?

Both of these datasets are available from the Harvard Geospatial Library (HGL):

• Toxics Release Inventory (TRI) Facilities, Massachusetts 2024
• Social Vulnerability Index (SVI) Overall Score by Census Tract, Massachusetts, 2020

In-class activity

Mock research question: Which facilities in our neighborhoods are the highest priority for intervention?

1. Click on the Toxics Release Inventory dataset.

2. Scroll down to the Description section of the metadata, and expand the information by selecting More Description.

💡 Discussion: Where did this dataset come from?

3. To learn more about the dataset, let’s look at the full metadata record. On the right-hand side of the data record in HGL, select the Metadata button.

4. Scroll down in the Metadata pop-up modal and find the following information:

• Spatial Reference Information → Grid Coordinate System Name
• Entity and Attribute Information → Attributes → Read through, e.g. F9__TRIFD

💡 Discussion: Why is this information important to know before using the dataset? Which variables are most useful for our investigation?

5. Back at the top of the screen in the map view, on the map click Click to Wake.

6. Click on one of the points on the map. Attribute information about the facility you selected will appear in a table below the map.

❓ Pause for questions.

Next steps demonstration in QGIS

The instructor will demo next steps in QGIS. Participants are not required to follow along, but can use the tutorial below to do so in-class, or later at home.

1. Download the Toxics Release Inventory (TRI) Facilities, Massachusetts 2024 from HGL or use the copy included in the demo_materials folder.

2. Open QGIS. (Download instructions)

3. Open a new Empty Project. Add a basemap.

4. Add the Toxics Release Inventory (downloaded to your computer) to the QGIS project by either: (1) dragging the file with the .shp file extension directly into the QGIS window from your file browser, or (2) using the menu navigation Layer → Add Layer → Add Vector Layer and using the Data Source Manager to select the file with the .shp file extension, then selecting Add and Close.

5. Zoom to the extent of the data by right-clicking the TRI data layer in the Layers panel and selecting Zoom to Layer.

6. Right-click the layer in the Layers panel again, and select Open Attribute Table. Observe the attributes, including F18__CHEMI, which we observed in the metadata refers to “Name of the chemical as listed on the TRI chemical list, or generic name, if the chemical is claimed as a trade secret.”

7. Close the attribute table and open the TRI layer properties by either (1) double-clicking on the layer in the Layers panel, or (2) right-clicking the layer in the Layers panel and selecting Properties.

8. Choose the Symbology menu. Click Single Symbol and select Categorized. From the drop-down arrow to the right of Value, choose the attribute to symbolize, F87__CARCI. Select Classify, and then OK.

💡 Discussion: What other questions could we investigate with this dataset? Which other spatial datasets might we layer this with this one to better understand?