Navigation
Using demographic data and spatial mapping to identify disparities in resource distribution and social justice.
Why does your zip code often predict your health better than your genetic code? In this lesson, we use the power of spatial data to reveal the hidden 'geography of opportunity'—or the lack thereof.
To identify social injustice, we start with Census Tracts—small, relatively permanent statistical subdivisions of a county. We look for Food Deserts, defined as low-income census tracts where a substantial number of residents have low access to a supermarket. In urban areas, this usually means the nearest grocery store is more than 1 mile away. By layering Demographic Variables like median household income () and vehicle availability (), we can calculate a Vulnerability Index. If is low and distance to food is high, the community is at high risk for food insecurity. GIS allows us to move beyond simple lists and see exactly where these 'deserts' bloom on a map.
Follow these steps to identify a target area:
1. Filter census tracts where Median Income $I < \$35,000$.
2. Create a Buffer Zone of 1 mile around all registered supermarkets.
3. Use the Erase Tool to remove the buffered areas from your census map.
4. The remaining polygons represent areas with high poverty and low food access.
Quick Check
In an urban GIS model, what is the standard distance threshold used to define 'low access' to food for a census tract?
Answer
1 mile (or approximately 1.6 kilometers).
Comparing income and canopy: 1. Generate a heat map of tree canopy density across the city. 2. Overlay a choropleth map of median household income. 3. Identify 'Cold Spots'—areas where income is in the bottom 20% and canopy density is also in the bottom 20%. 4. Use a scatter plot to check if the relationship is linear: .
Quick Check
If a map shows a 'hot spot' of high income overlapping with a 'cold spot' of green space, what does this suggest about the neighborhood's development?
Answer
It suggests a highly urbanized, wealthy commercial or residential area that lacks environmental amenities despite its economic status.
Calculate the priority for a new clinic: 1. Map population density () using a 100m grid. 2. Use Network Analyst to find all areas within a 15-minute bus ride of existing clinics. 3. Identify 'Service Gaps': High-density areas () outside the 15-minute transit zone. 4. Rank these gaps by the percentage of residents without private vehicles to determine the optimal location for the next facility.
Which GIS tool would you use to find areas that are NOT within a certain distance of a service?
In the formula , what does an value of indicate?
Straight-line distance (Euclidean) is the most accurate way to measure social equity in access to public transit.
Review Tomorrow
In 24 hours, try to explain the difference between a 'buffer' and 'network analysis' to a peer, and why it matters for social justice.
Practice Activity
Find a map of your local city and identify one 'amenity' (like a library) and one 'disamenity' (like a highway). Observe which neighborhoods they are located in.