Show HN: Remap – bike routing that builds loops from the best roads, on-device

Hey HN, excited to show you something I've been working on for a couple of years. I'm a passionate road cyclist and a former fruit company engineer. Today, there are two primary ways of knowing where to ride your bike: user-uploaded GPX files and generating routes via heatmap data. Both seemed inadequate to me after I was burnt countless times by being sent down high-speed roads or farm tracks.

When I want to go for a ride I have a specific time window in mind, and my goal is to get out and see nature and experience that unique feeling of freedom and joy that comes from riding a bike. So I built the tool of my dreams.

Remap reads the traffic levels, max speeds and road surface quality around you, then calibrates what road comfort means for your area. This leads to users getting comfortable routes out of the box automatically. Plenty of options are also available since cycling is a very opinionated sport.

The other important aspect of Remap is that it identifies what I've been calling 'lines' - sections of road that are excellent for cycling. Broadly speaking they need to be long, surrounded by nature and be away from traffic.

A great ride is full of lines, no ride is perfect end to end, but the more lines a ride has the better it feels. The other part of a great ride is that it should let you explore as wide as possible around where you start from, hit nature as much as possible, give you a climb here and there if you want, and not repeat any roads coming back - so it should ideally be a broad loop. Trying to fit all of this into an unpredictable road network with road rules and a set target distance alongside a large list of user-customisable routing preferences is a tall order, but I've succeeded in building something I'm immensely happy with, and I've been riding all summer with routes generated by Remap. It's been banger after banger ride.

Under the hood, it's a shared Rust core between web and iOS. Probably the most interesting part is route generation occurs locally on-device. I made this decision early on since I knew that this would be very expensive in terms of compute. The routing graph is a highly compressed columnar db that is able to be streamed directly to devices or browsers and be stitched across boundaries to provide a complete road graph. Routing tiles are fetched in Hilbert order so that multiple tiles in the same vicinity can be coalesced together. The architecture was inspired by Brandon Liu's pmtiles project which I'm a big fan of.

After the client has assembled its slice of the graph, it then explores it extensively. Much more deeply than traditional server-based routing software allows, since we have much more compute available we can examine all the side streets and roads that are relevant for delivering optimal bike routes. Using contraction hierarchies or some other optimisation designed for car navigation would defeat the purpose as bikes don't drop into arterials and then back out again like cars do.

The final point of Remap is that it makes solo riding social. You can't always schedule a group ride easily and whilst it's nice to ride solo, I often miss that social element. Since every ride built strings together lines, those lines are valuable and can be owned and claimed by players. The more you ride, the more 'watts' you earn to defend your lines.

I've got a full-time fuzzer going which hits up different cities and generates routes trying to catch out dive-bombs (unnecessary short detours), spurs (pointless out and back sections), various other anomolies. It's been running for a few weeks and caught some good bugs, but I'm really looking for real-world use right now. It's free to use, has a desktop and mobile site, as well as native iOS app. The native iOS app is fastest at route generation but the WASM isn't that far behind. Give it a go and let me know how you fare. Thanks HN!