⛰️ Topography Analysis
Explore the terrain and elevation profile surrounding transit stations. This tool uses USGS 3D Elevation Program (3DEP) high-resolution data to map slope, hillshade, and walkability constraints within a ½-mile radius of each station. Steep terrain can significantly limit the effective catchment area of a station — even when the street grid is otherwise well connected.
Terrain Analysis
About Topography Analysis
This tool analyzes the elevation and slope of the terrain surrounding transit stations using lidar-derived elevation models from the USGS 3D Elevation Program (3DEP), the most accurate publicly available source of high-resolution elevation data in the United States.
What We Measure
The analysis covers a ½-mile radius around each station — the standard walk-shed used in transit planning — and computes the following:
Elevation Range
- Minimum, maximum, mean, and total range of elevation within the walk-shed
- A larger elevation range indicates more topographic variation
Slope Classification
- Flat / Easy (0–2°) — level ground, accessible to all
- Gentle (2–5°) — slight incline, comfortable for most pedestrians
- Moderate (5–8.3°) — noticeable grade, some effort required
- Challenging (>8.3°) — exceeds the ADA outdoor ramp maximum; significant barrier for many
ADA Compliance Proxy
- The ADA outdoor maximum ramp grade is 8.33% (approximately 8.33°)
- Any terrain steeper than this threshold may be impassable for wheelchair users or people with limited mobility, even if sidewalks are present
- The percentage of the walk-shed exceeding this threshold is reported as an accessibility constraint indicator
Data Source
Elevation data comes from the USGS 3D Elevation Program (3DEP) at 10-meter resolution. 3DEP uses airborne lidar to produce bare-earth digital elevation models (DEMs) that remove buildings and vegetation, revealing the true ground surface. Slopes are computed from DEM gradients rather than a separate slope layer, which improves consistency across regions.
Why Terrain Matters for Transit
Slope is one of the least-studied but most consequential factors in transit access. A steep hill between a station and a neighborhood can effectively cut off walking access even when the straight-line distance is well within a half-mile. Research consistently shows that pedestrians treat uphill grades as significantly longer than the actual distance, reducing trip rates and increasing car use. For transit agencies, this means that terrain analysis can reveal hidden catchment constraints that street network analysis alone would miss.
This is particularly important for equity analysis. Neighborhoods with significant terrain barriers often rely on transit most heavily while facing the greatest walking barriers — making investment in accessible routes (ramps, elevators, level alternatives) especially valuable.
Important Notes
Data availability: 3DEP coverage is nationwide but resolution varies by region. Metropolitan areas typically have 1m or 10m data; rural areas may have 30m. This tool uses 10m resolution as the default.
Terrain vs. sidewalks: Slope analysis reflects the ground surface, not the walking surface. Ramps, switchbacks, stairs, and accessible routes are not captured in the terrain model.
Generation time: Elevation data is fetched directly from USGS servers, which takes approximately 30–90 seconds per station. Results are cached after the first run, so future loads are instant.