Why OpenAerialMap failed where OpenStreetMap succeeded

OpenStreetMap (OSM) is an ambitious project: creating a crowd-sourced, user-editable, free vector map of the world's roads, footpaths, and trails. Despite the scale of the task it has been remarkably successful, with more than 100,000 registered users and more than 29,000,000 ways. In 2007, a group of interested OSM users set out to do the same thing for raster-based satellite and aerial photography that OSM did for road data — but that project, OpenAerialMap (OAM), never reached the same level of success, and closed its doors in December of 2008. Looking back, OAM's creator finds both technical and social causes for the project's fate, and lessons for the future.

Christopher Schmidt launched OAM in hopes of building a free replacement for the copyrighted satellite image layer used by Google Maps. The OSM project had struck a deal with Yahoo to permit usage of Yahoo's aerial image layer in the Potlatch map editor, but only for the purpose of editing GPS traces against a satellite background image: the data was to remain Yahoo's and it could not be displayed in the OSM web map. A sister project, OpenTopoMap, attempted to do the same thing for topographic map data, using a similar methodology, but Schmidt put the greater effort into OAM due to its presumably wider user-appeal.

OAM's initial map set was a Landsat layer donated by i-Cubed. Where aerial photography was available, OAM would support that instead thanks to its greatly increased resolution. The project chose to store its map tiles as uncompressed GeoTIFF images in the standardized EPSG:4326 map projection; that way, although more storage space was required than for a compressed format, the openaerialmap.org server could serve up map tiles without worrying about the CPU overhead of converting every tile served.

By the middle of 2008, however, things had started to slow down. Although there were scores of free, often public-domain aerial data sets, they were not organized or easy to work with: many in the U.S. belonged to individual state or county government projects, running on legacy systems — if online at all — in different projections, and in inconvenient file formats like the proprietary MrSID. On top of that, the data began to grow faster than the disk space on the donated server could keep up with.

The technical dimension

By the time Schmidt decided to pull the plug on the project, he had uploaded ten terabytes of map data, which was only a fraction of what was available — the U.S. Geological Survey (USGS) generously offered to donate its entire aerial data set of the United States, which would have taken up more than 100 terabytes of compressed storage.

It is possible that a benefactor could have been found to donate storage hardware, but that was not the only technical hurdle. Converting the data sets from their original form into the standard adopted by OAM was a time-consuming process, and one that varied from data set to data set, Schmdit said. "We wanted to have large mosaics, EPSG:4326 projected, as GeoTIFFs. Building that kind of tileset out of hundreds, or thousands, of small MrSID files requires significant resources. Just loading MrSID itself can be a beast since MrSID is closed source and not built into many tools."

MrSID (mutli-resolution seamless image database) is a wavelet-based geographic image file format, created and patented by map software company LizardTech. Each file can be extracted in multiple resolutions and quality levels, and sub-blocks of the image can be extracted without reading the entire file. The format is popular in commercial applications, but there is no open source implementation. Several free tools can decode MrSID to convert it to other formats.

In contrast to the process required to convert a MrSID archive to GeoTIFF, OpenStreetMap map-making requires the comparatively straightforward conversion of GPS traces to OSM ways. From the beginning of OAM, Schmidt undertook the lion's share of this "technical gruntwork" himself, rather than building software tools to automate the process for end users. In retrospect, he reflected, that decision severely hindered the development of a community around the project. "The system was simply not designed for users, because it was kind of a one man show. My lack of delegation skills is apparent in many of the things I do :)." A handful of users got up to speed on the conversion process, he added, but most simply gave pointers to available data sets and waited for someone else to take care of them.

The social dimension

Without easy-to-use conversion tools, the number of contributors to the project remained low, but, Schmidt said, the task of building a raster graphics map did not lend itself towards community participation either. In OSM, large data set imports are rare; the majority of the contributions come from individual users collecting GPS traces of their local surroundings, and editing their local map.

In spite of having similar goals, OAM found itself in almost the exact opposite situation. "Aerial imagery gathering doesn't lend itself to crowdsourcing the same way vector data gathering does," Schmidt said, "Almost all of your data is going to be big dumps from state agencies and the like." A few users collected their own aerial photos with kites or drones, he said, but their images amounted to just a tiny fraction of the total.

"I think the important thing is to let people take ownership of what they're doing," Schmidt remarked. Without the level of direct participation found in the OSM project, users did not feel like they "owned" the final product. "Looking back, I can see a lot of places to build community, but at the time, I wasn't really interested in building a community, and by the time that I realized I was burnt out, there was already an expectation that things would just 'magically happen'." Consequently, when Schmidt decided he was burnt out, there was no one else ready to take on the task of stewarding the project.

The next level

Although he switched off the openaerialmap.org tile server in December 2008, Schmidt has not stopped thinking about OAM, and how to grow a community around it. "The desire for easy to find an access aerial imagery is definitely there. The continued interest in OAM even after the web frontend essentially stopped working speaks to that, and the continued attempts to participate even with terrible documentation, poor setup, etc."

He is considering re-launching the project with a different set of goals and different ways of attracting user participation, placing less emphasis on serving as a single-source repository of image tiles. Instead, OAM could function like a directory for the existing aerial imagery map sets hosted elsewhere, like the approach taken by Web Map Service (WMS) directory wms-sites.com. Such a service would be almost as useful as serving the tiles themselves, he said, since so much of the difficulty now is in finding the data set for a particular area.

Building a wiki-like directory that points to data hosted elsewhere might also allow users to build "ownership" of their contributions, Schmidt added. "The imagery is only a first step towards the end result. Does the imagery have metadata about it? Is it aligned properly? Do people know how to find it?" Most often, he said, the only way to find a data set is search the web, and then the results have no user interface, "just an open FTP site linked from one page under 'GIS Data'."

The mapping agencies are usually helpful, he said, but do not have the manpower or IT resources to run a WMS or tile server. "This is why I'm thinking a catalog approach might work: if you let the people who maintain this imagery at places like MassGIS contribute to a site information *about* the imagery — concentrating on things like quality, capture dates, etc. — you can have them have a product they can feel like they're the owner of."

Although he has not taken any formal steps toward this goal, it is undeniable that there is latent interest in resurrecting the OAM project in some form. The map server is down, but the OAM wiki remains up, and other users have started a discussion page to brainstorm ideas for the future of the project. Its main archive is off-line, but people continue to find the mailing list via third-party sites and write in to ask questions.

Rarely does an open source software project that has failed to get off the ground take a serious look at why — although the benefits of doing so are clear. Schmidt's assessments of what went wrong with the first incarnation of OAM will help make the next effort more technically prepared, and better matched to the user community it needs in order to build up critical mass and thrive. Similarly, looking back at how the practical differences between raster and vector mapping led OAM down a completely different path than OSM (in spite of their seemingly similar goals) is an object lesson other projects would be wise to study as well.