Using KML Files

These instructions are for downloading data files to display on Google Earth, which is how Curvature was originally shared with the world. While most users will likely use the map that you can view in your web browser, these downloadable files may be of interest for Google Earth users, offline viewing, or other purposes.

Curvature file for New York State as shown in Google Earth.

The Curvature program generates zipped KML map files (with a .kmz file extension) that can be viewed in Google Earth. These map files are generated for all regions of the world and are refreshed every month or so to take into account updates to the underlying data sourced from the OpenStreetMap.

Step 1: Install Google Earth

To view Curvature KML files, you will first need to install Google Earth on your computer. Google Earth is a free program available for both desktop computers as well as mobile devices.

Step 2: Download a Curvature KML file

Head to https://kml.roadcurvature.com/ to download a compressed KML file for a region. The KML files are ordered by continent, country, and state/province. Curvature produces three levels of data files:

c_1000: these files highlight the most twisty roads
c_300: these files include less twisty roads in addition to the most twisty roads
c_1000.curves: these files highlight individual road segments (as described on the Detected Curves KML Files page)

Most people will want to download the “c_1000” version of the files as these highlight only the most twisty roads — those with approximately 1km or more of curves.

Click on the “c_1000” link to download the file to your computer. Usually it will end up in a “Downloads” folder on your computer.

Step 3: Open the KML file in Google Earth

Find the KML file in your downloads folder. It will be named something like “vermont.c_1000.kmz”.

Double click on it to open it in Google Earth. If for some reason it doesn’t open, first open Google Earth and choose “File » Open…” and select the file.

4. Look for curvy roads

After you’ve opened the file in Google Earth you can zoom around and identify curvy roads:

The "vermont.c_1000.kmz" file loaded in Google Earth. — The “vermont.c_1000.kmz” file loaded in Google Earth.

Clicking on a road will pop up details indicating any surface tags for each segment as well as length and curvature value:

Clicking on a highlighted road will pull up details.

What are curvature values?
Curvature values are a weighted measure of length of curves in the roadway (expressed as meters). Based on my experience looking at the data and riding the roads, I’ve found that the curvature values regularly correlate to how much fun I have riding the road — assuming a good road-surface, low traffic and not too many stop-signs.

curvature: < 300
There might be a few fun corners on these, but these roads are predominantly straight or have long distances between each significant curve.
curvature: 300-1,000
These roads have several significant corners close together. They aren’t likely touring destinations unless you’re stuck with otherwise straight roads in the region, but if you are looking to spice up your commute with a few corners, these might be more fun than the most direct route.
curvature: 1,000-3,000
This range has a lot of fun roads. They’ll usually have a few dozen corners and generally feel more winding than straight.
curvature: 3,000-10,000
For much of the world, this range includes the destinations roads that people may ride for hours in order to visit. These roads will usually have long sections of tight turns often for miles on end. In the northeastern US, the best roads are all in this range.
curvature: 10,000+
These are truly epic roads with mile upon mile of twists and turns.

Step 5: Plan your route

Google Earth doesn’t have great built-in route-planning tools, so it is usually easiest to simply identify the curvy roads via the Curvature files in Google Earth, then plan your route using other route-planning software such as Garmin Base Camp, Google Maps, or similar.