1. Portals

• Explore open data portals and learn how to use them to find GIS data
• Explore how content may be organized and how to refine searching

In class activity

Consider this request a student made to the Harvard Map Collection for help with finding GIS data in 2024:

“I would like to create a GIS map of food deserts in DC by layering maps of grocery store locations, corner store locations, and other options found on Open Data DC with census data to identify areas where large populations do not have access to healthy foods.”

Where is a good place to get started searching for food desert data in DC?

1. In a web browser, search for “GIS open data portal DC”.

2. Visit opendata.dc.gov.

3. Scroll down and find the search bar that says “Search for apps, maps, documents, data and stories…”. Place your cursor in the search bar and click Enter. This will bring you to a results page with all items, and filters you can use to refine your search.

4. Under Type select Feature Service. It is a trend that many open data portals host GIS data layers as streaming “feature services”, which are displayed in web maps. From these feature service landing pages, you can often download the data in various common geospatial formats, such as shapefile or geoJSON. Using type facets and filtering data by shapefile, geojsons, point, line, or polygon or feature service are a good way to tell the search portal you are looking for geospatial data, as opposed to spreadsheets, PDFs, or other kinds of information.

5. Click a random result, and observe how the feature service landing page is structured. What are your observations? How would you download this data, in order to bring it into a GIS?

6. Return to the results list, filtered by Feature Service. Search for relevant terms food, grocery, corner stores, and observe which datasets are available which could be useful to the project.

Demo and explore more

Sample data

You can download and explore sample datasets related to this activity from the workshop data homepage, hosted on the Open Science Framework (OSF.io)

1. Visit the workshop data homepage.

2. Click the three vertical dots icon and select Download.

3. The folder that downloads to your computer contains sample data from all the workshop activities. It is a zipped or compressed file. In order to use it, you will have to double-click it on Mac or right-click → Extract or Uncompress on a PC.

Follow-along steps

How did we access the sample data, and how do we learn to understand and use it?

1. From Open Data DC, search for food and filter by feature service.

2. To understand the data and how it is structured, click View Full Details, which brings us to this documentation page.

3. To download as GIS data, select the Download button in the left-hand sidebar, and choose GeoJSON or Shapefile.

4. To use the data in QGIS, extract or unzip the shapefile, and drag the file ending in .shp into the QGIS document. Alternatively, you can drag the .geoJSON file into the QGIS document. Another way to add vector data to a QGIS project is use the menu on the top bar Layers → Add Layers → Add Vector Layers and select the file ending in .shp.

Why are there so many files associated with a shapefile? You can learn more.

5. Right-click Low_Food_Access_Areas in the Layers pane and click Open Attribute Table to see how the table matches up with the “View Full Details” documentation from the portal.

6. Right-click Low_Food_Access_Areas in the Layers pane → Properties → Symbology → Click Single symbol to change it to Graduated → Value = PRTUND185 → Classify (notice under Mode there are many classification options. Be aware of which you’re choosing by reading about each method) → OK.