flattensf.com finds the flattest route between two points in San Francisco
flattensf.com, a page credited to Drew Edwards, plans routes between two points in San Francisco and lets the user decide how much hill to accept. The routing runs in the user's browser, over more than 160,000 street segments. Elevation comes from USGS 1 m lidar, and the street network from the Overture / OpenStreetMap street graph.
The central control is a slider. It runs along the whole trade-off between distance and climbing: every route that nothing else beats on both counts, from the shortest path to the flattest one worth walking. The flat end has a defined limit. It is the point where a foot of climb costs 200 ft of walking, and the page says that beyond that the routes stop being routes. Moving the slider right never shortens the route and never adds climbing, so each step trades a longer trip for less uphill.
Some details of how the numbers work. Climbing is counted as cumulative gain, not the net difference between the two endpoints, so a route that goes up and down still accrues every climb along the way. Stairways are allowed for walking and excluded for biking. The page also draws faint lines for the other routes along the way, so the user can see the alternatives around the chosen one.
Place search works offline: street intersections, places and addresses for San Francisco are built into the page. The page ends with a link labelled "Source, data and the full analysis".
Key facts
- Routes are computed in the user's browser over more than 160,000 San Francisco street segments.
- Elevation comes from USGS 1 m lidar; streets come from the Overture / OpenStreetMap street graph.
- A slider covers every route that nothing else beats on both distance and climbing, from the shortest path to the flattest one worth walking.
- The flattest end is where a foot of climb costs 200 ft of walking; sliding right never shortens the route and never adds climbing.
- Climbing means cumulative gain, not net difference between endpoints; stairways are allowed on foot and excluded on a bike.
Why it matters
Anyone who has planned a walk or ride in San Francisco knows the shortest route is often the steepest. This tool makes the trade explicit instead of hiding it in a single suggested route. Rather than returning one answer, it shows the full range of sensible options between the shortest path and the flattest one worth walking, and the user picks a point on that range. The fine elevation data (USGS 1 m lidar) is what makes street-level climbing figures possible.
Who it affects
Pedestrians and cyclists in San Francisco, especially anyone who wants to avoid steep climbs and is willing to walk or ride farther to do it. The page treats the two modes differently: stairways are allowed on foot and excluded on a bike.
How to use it
Open flattensf.com and find the start and end points with the built-in place search, which covers San Francisco street intersections, places and addresses and works offline. Then move the slider. Toward the left you get the shortest path; toward the right the route gets longer and flatter, up to the point where a foot of climb costs 200 ft of walking. Faint lines show the other routes along the way. Everything runs in the browser.
How solid is it
The page states its method and its data sources plainly: USGS 1 m lidar for elevation, the Overture / OpenStreetMap street graph for streets, and more than 160,000 street segments. It also points to a link labelled "Source, data and the full analysis". The text does not give an example route or the amount of climb saved, so how much a typical trip improves is not something the page itself shows in this text.
Risks and caveats
The tool covers San Francisco only. Climbing is cumulative gain, so a route that goes up and down counts every climb, not just the difference between start and finish. The flat end is bounded: past the point where a foot of climb costs 200 ft of walking, the page says the routes stop being routes. The text does not say which year or release of the USGS lidar is used.
“Sliding right never shortens the route and never adds climbing.”
— flattensf.com