Tracing Satellite Imagery in OpenStreetMap

March 17 2012 by Ian Villeda

For the past two weeks we have been tracing satellite imagery into OpenStreetMap to support some of our subscribers using MapBox Streets. OpenStreetMap’s real power is that if something isn’t on the map, you can just add it. So this is more than just open data for us, this is about co-creation and collaborating with a larger community.

The sprint table Around the sprint table at the MapBox office in Washington DC

The fact that the geography around us is constantly changing is why we are using OpenStreetMap to power our key maps. Not only does OpenStreetMap have amazing data today - every day the data improves as the its network of contributors grows. Right now, our team is focusing on completing a few key populous cities, making sure that suburbs and popular features like buildings, rivers, and parks provide meaningful and attractive context for users. With a team of six people heads down we can very quickly light up a city and meet other local contributors working on the ground.

Guadalajara Tracing A look at new edits over the last week to Guadalajara, Mexico, a huge city with the metropolitan area of over 4 million people.

The Tools to Start Tracing

To add all of these features, we’re using JOSM an open source desktop editor for OpenStreetMap. Here is a quick step by step of how you can start tracing imagery in 5 minutes using the same tools and processes we are.

Before you start tracing, be sure to read the OpenStreetMap editing standards and conventions, then download JOSM. It’s helpful to have a mouse on hand (versus a trackpad), as you’ll want to do a lot of precise clicking. Once you’ve set up and run JOSM, click the ‘download data’ button at the top left.

downloading data from JOSM

You will see a map similar to openstreetmap.org. Find and select the area you are interested in and click download. To pan around the map, press and hold CTRL. To select an area, just use the left mouse button.

bounding box for data downloads into JOSM

To edit, add Bing Imagery under the Imagery dropdown menu.

Bing Imagery in JOSM

You’ll then want to toggle between JOSM’s three modes using these key bindings: draw (A), select (S), and delete (D). Use draw to add nodes, ways and areas. When you’re done adding a way, double click on the last node. To create an area simply close a series of nodes by attaching the last node the the first. For more advanced editing, check out the online guide and useful plugins.

Once you’ve created your features, tag them appropriately with a preset (see ‘Presets’ menu) or directly via the ‘Properties’ window (see ‘Windows’ menu). Good resources for learning how to tag elements in OpenStreetMap include TagInfo and the Map Features page of the OSM wiki. Explore the various list-serves and engage others in the OSM community.

Now you’re ready to map the world.

Designing your Map

If you are looking to create your own custom designed map of OpenStreetMap data, it is easy to do so. Once your data is in OpenStreetMap, download TileMill, the open source design studio then read “Create a custom map of your city in 30 minutes with TileMill and OpenStreetMap”. You will be able to make maps that look a lot like MapBox Streets and host them on your own MapBox account, with even free plans. If you have questions post them to support.mapbox.com.