OpenStreetMap is a marvel of modern crowdsourcing. Since its creation in 2004, DIY cartographers – typically armed with GPS devices or satellite photography – have been slowly mapping the world's road networks and landmarks to create a free alternative to proprietary geographic data that can then support tools like trip planners. The process, which began in the U.K., is painstaking and piecemeal, and nearly a decade into it, more than a million people have contributed a sliver of road here or a surveyed cul-de-sac there.

Academics refer to this kind of collaborative mapmaking as "volunteered geographic information," and OpenStreetMap is one of the most successful examples of it out there. Research into the system suggests that these amateur maps are impressively accurate in communities dense with contributors (like Germany: Germans love OpenStreetMap). But until now, it's been much easier to assess how good these maps are than to ask how they got that way.

Now, researchers are getting much better at processing OpenStreetMap's data to access its history. The above historic timelapse comes from a study, published in the journal Spatial Statistics, that retraced the growth of OpenStreetMap networks in three areas of Ireland to understand how the networks are built. This is the full visual history of the expansion of OpenStreetMap in Maynooth, Ireland, from January of 2007 through January of 2011:

That evolution looks an awful lot like how physical street networks themselves evolve over time. And, in fact, the Irish researchers behind this project found that OpenStreetMap expands precisely through two processes – "exploration" at the outer edges of the known network, and concurrent "densification" of its core – that have been used to describe how road networks are built.

"In a sense, there’s a parallel between how cities grow in reality and how they are mapped," says Padraig Corcoran, one of the study's authors. This is probably not a coincidence. "It kind of suggests there might be some underlying process which governs the growth of networks in general, irrespective of what they represent," Corcoran adds.

And this could be true of social networks, street networks or networks of digital data. If you look at your own social network, for instance, your circle of friends expands outward as one friend introduces you to another, who introduces you to yet another person not already in your network. At the same time, though, your social network may also be growing "denser," as you meet people already connected to other friends that you know (i.e., the boyfriend of your roommate, who happens to also be the coworker of your college friend).

On OpenStreetMap, this is what that process looks like (again, in Maynooth), where the densification is represented in green and the exploration in red:

Obviously, a new area must be explored before anyone can build out that particular neighborhood's spiderweb-like side streets. But these two processes occur simultaneously in different parts of the network. Given that OpenStreetMap appears to so closely mirror the growth of real-world infrastructure, the tool may offer the opportunity to understand the expansion of networks in a way that no one was trying to do when these streets were paved in the first place.

Researchers have gone back to look at earlier maps of development. But that process typically involves digging out old paper maps, scanning and digitizing them. And good time stamps aren't always available to pinpoint a map's moment in time. But with OpenStreetMap, Corcoran says, "It opens an opportunity to study how networks are growing in real time. OpenStreetMap is currently an evolving process – it's still not complete. We don’t know when it will reach a stage of maturity."

All of the impressively intricate work it will take to get there raises another question that research has not yet answered about this crowdsourced process: Why are all of these people doing this?

"We don’t really know what motivates people," Corcoran says. When people register to contribute to OpenStreetMap, the site doesn't ask them why they want to participate.  "Some of the reasons people suggest is that people like to be part of a community, like to map their own area, they like to make contributions to society, to provide data that's of use to society," Corcoran says. Because there's no central authority assigning tasks or coordinating all those contributors, it seems all the more impressive that they somehow self-organize according to the same principles that entire cities exhibit when they expand over time.

2012 was the year in which a wide audience began to understand the process behind making maps -- and that it's a massive, global effort in the pursuit of better and more complete map data. OpenStreetMap, a collaborative, open data process for making maps, has continued its fast growth last year hitting its million contributors mark.

At MapBox, we believe that the collaborative approach of OpenStreetMap is the future of mapping. By adopting local knowledge and local management of data, it's possible to build a complete, accurate, and freer map of the world. How OpenStreetMap gets its data is essential -- the most trusted source is always on the ground, with GPS units and local knowledge. But for much of the world, this isn't an immediate option because of distance and time. Instead, home users edit the map, referencing GPS tracks made by others and satellite data. So far, this has been a tricky process. OpenStreetMap's editing tools are complex and do little to help users understand details like road classifications. We want tools for contributing map data to be accessible to anyone, in any language, with any level of computing skill.

That's why we're building iD, a new map editor for OpenStreetMap. iD is being built with a focus on design, which means understanding and analyzing similar tools and iterating through different ways of solving the same problem -- deciding whether it's useful to adopt patterns from graphics editors, web maps, or games in different parts of the interface.

We're designing a UI that's simple and friendly, with a uniform "finished" look that makes it approachable and understandable for new users. It's extremely important that Saman Bemel Benrud, the lead designer, is pushing the design process in concert with development, so that we can think of user experience in its totality rather than just as design tasks.

The little things matter. As Saman wrote, details like custom mouse cursors make the editing process more intuitive and obvious to users, as well as less dependent on help documentation. The goal for this editor is for it to become the default on OpenStreetMap.org, where it will be used by hundreds of thousands of users, so accessibility is a top priority.

Similarily, integrated documentation is a priority from the get go. We use the excellenttaginfo service that provides community-sourced documentation through an API to provide inline guidance. For instance, we only offer classifications that make sense in a given situation, and we are starting to build out inline help.

We're also pushing the limits of technology for iD, since it's one of the first tools of its kind. We've been testing and tuning graphics performance in browsers so that map features are recognizable from normal web maps and fast to change. iD is heavily tested, because we know that map data needs to be trusted and so our tools need to be trusted to work exactly as expected.

At the end of 2012, we released iD alpha0, a first version with the ability to make all basic edits such as drawing roads, tagging houses and monuments, and refining the work of others.

All of the work on iD is in the open on a repository on GitHub, including issues that we're currently working on and the roadmap for the next three months. We also maintain atesting instance so you can try it out yourself, and a blog that includes many lessons learned from the project. Finally, this video walks through how you can use iD to make edits to OpenStreetMap.

Tom MacWright specializes in building interactive and creative open source mapping tools for MapBox. He is a lead architect of our open source mapping stack, including TileMill, which combines Mapnik, Carto, Modest Maps, and other open source tools in a simple interface for designing custom maps. He's also the lead developer behind Wax, a collection of map utilities, and key to our Knight Foundation funded work to make OpenStreetMap easier to edit and use.