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A new web tool called Flatten SF calculates the flattest walking and biking routes across San Francisco. It uses USGS lidar elevation data and OpenStreetMap graphs to offer a trade-off between distance and climbing. The tool allows users to visualize routes that minimize elevation gain, addressing the city’s notorious steep terrain.
San Francisco residents and visitors now have access to Flatten SF, a new web-based tool designed to identify the flattest walking and biking routes between any two points in the city. Developed by Drew Edwards, the application leverages USGS 1-meter lidar elevation data and the OpenStreetMap street graph to compute paths that minimize cumulative climbing. This development addresses a persistent challenge for pedestrians and cyclists navigating San Francisco’s steep topography, offering a practical alternative to standard shortest-path navigation apps.
The tool operates entirely within the user’s browser, processing data across approximately 160,000 street segments. According to the project description, the algorithm generates a slider that allows users to adjust the trade-off between distance and climbing. As the slider moves, it displays every route that is not beaten by another route on both distance and elevation gain metrics. This ensures that users can see the full spectrum of options, from the shortest possible path to the flattest route deemed practical for walking.
A key feature of the calculation is the definition of “climbing.” The tool measures cumulative elevation gain rather than the net difference between the starting and ending points. This distinction is critical in San Francisco, where a route might start and end at the same elevation but involve significant uphill and downhill travel. The tool also differentiates between modes of transport: stairways are included for walking routes but are excluded for biking routes, reflecting the physical realities of navigating the city’s infrastructure.
The interface includes a place search function that works offline, with street intersections, places, and addresses for San Francisco built directly into the page. Faint lines on the map display alternative routes along the way, providing visual context for the trade-offs being made. The developer notes that sliding the control to the right never shortens the route and never adds climbing, ensuring a predictable user experience.
Addressing San Francisco’s Topographical Challenges
The launch of Flatten SF matters because it directly addresses one of the most significant barriers to active transportation in San Francisco: steep hills. Standard navigation apps typically prioritize distance or time, often routing pedestrians through steep inclines that are physically demanding or inaccessible for some users. By prioritizing elevation gain, this tool empowers individuals with mobility constraints, fitness limitations, or a preference for easier terrain to navigate the city more confidently.
For cyclists, the exclusion of stairways and the focus on cumulative gain provides a more accurate representation of effort required. This can influence route planning for daily commutes or recreational rides, potentially encouraging more people to choose biking or walking over driving. The tool’s reliance on high-resolution lidar data sets a new standard for accuracy in urban routing applications, demonstrating how open-source data can be used to solve specific local problems.
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Data Sources and Technical Framework
The project relies on two primary open data sources. The USGS National Map provides 1-meter lidar elevation data, offering precise topographical information for the city. This is combined with the Overture/OpenStreetMap street graph, which supplies the network of streets and pathways. The integration of these datasets allows for a granular analysis of the urban environment, capturing subtle elevation changes that coarser data sets might miss.
The development reflects a broader trend in civic technology, where local developers use open data to create niche tools that serve specific community needs. By processing the data in the browser, the tool avoids the need for server-side computation, making it accessible and responsive for users. The project is credited to Drew Edwards, who has made the source code, data, and full analysis available for public review.
“Routes are computed in your browser over 160,000 street segments, using USGS 1 m lidar elevation and the Overture / OpenStreetMap street graph.”
— Drew Edwards, developer of Flatten SF
Performance and Real-World Application Limits
While the tool is currently available, its real-world performance under varying network conditions and on older devices remains to be tested by a broader user base. The project documentation notes that routes are computed in the browser, which may impact loading times for complex queries or on devices with limited processing power. It is not yet clear how frequently the underlying OpenStreetMap data is updated in the tool, which could affect the accuracy of newly constructed paths or closed streets.
Additionally, the definition of a “flattest route worth walking” involves a specific threshold where a foot of climb costs 200 feet of walking. The subjective nature of this trade-off means that different users may find different points on the slider most useful. The tool does not currently account for real-time factors such as construction, temporary closures, or sidewalk conditions, which are critical for safe navigation.
Community Adoption and Potential Expansions
The next phase for Flatten SF involves community adoption and feedback. As more users test the tool, developers may identify bugs or areas for improvement in the routing algorithm. There is potential for integration with other apps or devices, such as smartwatches or dedicated cycling computers, which could expand its utility beyond the web browser.
Future updates might include real-time data integration to account for temporary obstacles or weather conditions. The open-source nature of the project also invites contributions from the tech community, potentially leading to versions of the tool for other cities with similar topographical challenges. Users are encouraged to verify specific route details with official city resources before relying on them for critical travel, especially in areas with ongoing construction.
Key Questions
How does Flatten SF calculate the flattest route?
It uses USGS 1-meter lidar elevation data combined with the OpenStreetMap street graph to calculate cumulative elevation gain across 160,000 street segments, allowing users to trade off distance for climbing.
Does the tool account for stairs?
Yes, but differently for each mode. Stairways are included in walking routes but are excluded from biking routes, reflecting the physical constraints of each mode of transport.
Is the place search function online?
No, the place search is offline. Street intersections, places, and addresses for San Francisco are built directly into the web page, allowing for quick searches without needing to query an external server.
What is the difference between net and cumulative climb?
Cumulative climb is the total elevation gained throughout the route, while net climb is the difference between the start and end elevations. Flatten SF uses cumulative climb, which better reflects the physical effort required.
Source: hn
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